🏗 Merge C++ into python codebase (#504)

## Description:

Move esphome-core codebase into esphome (and a bunch of other refactors). See https://github.com/esphome/feature-requests/issues/97

Yes this is a shit ton of work and no there's no way to automate it :( But it will be worth it 👍

Progress:
- Core support (file copy etc): 80%
- Base Abstractions (light, switch): ~50%
- Integrations: ~10%
- Working? Yes, (but only with ported components).

Other refactors:
- Moves all codegen related stuff into a single class: `esphome.codegen` (imported as `cg`)
- Rework coroutine syntax
- Move from `component/platform.py` to `domain/component.py` structure as with HA
- Move all defaults out of C++ and into config validation.
- Remove `make_...` helpers from Application class. Reason: Merge conflicts with every single new integration.
- Pointer Variables are stored globally instead of locally in setup(). Reason: stack size limit.

Future work:
- Rework const.py - Move all `CONF_...` into a conf class (usage `conf.UPDATE_INTERVAL` vs `CONF_UPDATE_INTERVAL`). Reason: Less convoluted import block
- Enable loading from `custom_components` folder.

**Related issue (if applicable):** https://github.com/esphome/feature-requests/issues/97

**Pull request in [esphome-docs](https://github.com/esphome/esphome-docs) with documentation (if applicable):** esphome/esphome-docs#<esphome-docs PR number goes here>

## Checklist:
  - [ ] The code change is tested and works locally.
  - [ ] Tests have been added to verify that the new code works (under `tests/` folder).

If user exposed functionality or configuration variables are added/changed:
  - [ ] Documentation added/updated in [esphomedocs](https://github.com/OttoWinter/esphomedocs).

esphome/components/adc/adc_sensor.cpp

@@ -0,0 +1,89 @@
+#include "esphome/components/adc/adc_sensor.h"
+#include "esphome/core/log.h"
+
+namespace esphome {
+namespace adc {
+
+static const char *TAG = "adc";
+
+ADCSensor::ADCSensor(const std::string &name, uint8_t pin, uint32_t update_interval)
+    : PollingSensorComponent(name, update_interval), pin_(pin) {}
+
+#ifdef ARDUINO_ARCH_ESP32
+void ADCSensor::set_attenuation(adc_attenuation_t attenuation) { this->attenuation_ = attenuation; }
+#endif
+
+void ADCSensor::setup() {
+  ESP_LOGCONFIG(TAG, "Setting up ADC '%s'...", this->get_name().c_str());
+  GPIOPin(this->pin_, INPUT).setup();
+
+#ifdef ARDUINO_ARCH_ESP32
+  analogSetPinAttenuation(this->pin_, this->attenuation_);
+#endif
+}
+void ADCSensor::dump_config() {
+  LOG_SENSOR("", "ADC Sensor", this);
+#ifdef ARDUINO_ARCH_ESP8266
+#ifdef USE_ADC_SENSOR_VCC
+  ESP_LOGCONFIG(TAG, "  Pin: VCC");
+#else
+  ESP_LOGCONFIG(TAG, "  Pin: %u", this->pin_);
+#endif
+#endif
+#ifdef ARDUINO_ARCH_ESP32
+  ESP_LOGCONFIG(TAG, "  Pin: %u", this->pin_);
+  switch (this->attenuation_) {
+    case ADC_0db:
+      ESP_LOGCONFIG(TAG, " Attenuation: 0db (max 1.1V)");
+      break;
+    case ADC_2_5db:
+      ESP_LOGCONFIG(TAG, " Attenuation: 2.5db (max 1.5V)");
+      break;
+    case ADC_6db:
+      ESP_LOGCONFIG(TAG, " Attenuation: 6db (max 2.2V)");
+      break;
+    case ADC_11db:
+      ESP_LOGCONFIG(TAG, " Attenuation: 11db (max 3.9V)");
+      break;
+  }
+#endif
+  LOG_UPDATE_INTERVAL(this);
+}
+float ADCSensor::get_setup_priority() const { return setup_priority::DATA; }
+void ADCSensor::update() {
+#ifdef ARDUINO_ARCH_ESP32
+  float value_v = analogRead(this->pin_) / 4095.0f;
+  switch (this->attenuation_) {
+    case ADC_0db:
+      value_v *= 1.1;
+      break;
+    case ADC_2_5db:
+      value_v *= 1.5;
+      break;
+    case ADC_6db:
+      value_v *= 2.2;
+      break;
+    case ADC_11db:
+      value_v *= 3.9;
+      break;
+  }
+#endif
+
+#ifdef ARDUINO_ARCH_ESP8266
+#ifdef USE_ADC_SENSOR_VCC
+  float value_v = ESP.getVcc() / 1024.0f;
+#else
+  float value_v = analogRead(this->pin_) / 1024.0f;
+#endif
+#endif
+
+  ESP_LOGD(TAG, "'%s': Got voltage=%.2fV", this->get_name().c_str(), value_v);
+
+  this->publish_state(value_v);
+}
+#ifdef ARDUINO_ARCH_ESP8266
+std::string ADCSensor::unique_id() { return get_mac_address() + "-adc"; }
+#endif
+
+}  // namespace adc
+}  // namespace esphome

esphome/components/adc/adc_sensor.h

@@ -0,0 +1,43 @@
+#pragma once
+
+#include "esphome/core/component.h"
+#include "esphome/core/esphal.h"
+#include "esphome/components/sensor/sensor.h"
+
+namespace esphome {
+namespace adc {
+
+class ADCSensor : public sensor::PollingSensorComponent {
+ public:
+  /// Construct the ADCSensor with the provided pin and update interval in ms.
+  explicit ADCSensor(const std::string &name, uint8_t pin, uint32_t update_interval);
+
+#ifdef ARDUINO_ARCH_ESP32
+  /// Set the attenuation for this pin. Only available on the ESP32.
+  void set_attenuation(adc_attenuation_t attenuation);
+#endif
+
+  // ========== INTERNAL METHODS ==========
+  // (In most use cases you won't need these)
+  /// Update adc values.
+  void update() override;
+  /// Setup ADc
+  void setup() override;
+  void dump_config() override;
+  /// `HARDWARE_LATE` setup priority.
+  float get_setup_priority() const override;
+
+#ifdef ARDUINO_ARCH_ESP8266
+  std::string unique_id() override;
+#endif
+
+ protected:
+  uint8_t pin_;
+
+#ifdef ARDUINO_ARCH_ESP32
+  adc_attenuation_t attenuation_{ADC_0db};
+#endif
+};
+
+}  // namespace adc
+}  // namespace esphome

esphome/components/adc/sensor.py

@@ -0,0 +1,52 @@
+import esphome.codegen as cg
+import esphome.config_validation as cv
+from esphome import pins
+from esphome.components import sensor
+from esphome.const import CONF_ATTENUATION, CONF_ID, CONF_NAME, CONF_PIN, CONF_UPDATE_INTERVAL, \
+    CONF_ICON, ICON_FLASH, CONF_UNIT_OF_MEASUREMENT, UNIT_VOLT, CONF_ACCURACY_DECIMALS
+
+ATTENUATION_MODES = {
+    '0db': cg.global_ns.ADC_0db,
+    '2.5db': cg.global_ns.ADC_2_5db,
+    '6db': cg.global_ns.ADC_6db,
+    '11db': cg.global_ns.ADC_11db,
+}
+
+
+def validate_adc_pin(value):
+    vcc = str(value).upper()
+    if vcc == 'VCC':
+        return cv.only_on_esp8266(vcc)
+    return pins.analog_pin(value)
+
+
+adc_ns = cg.esphome_ns.namespace('adc')
+ADCSensor = adc_ns.class_('ADCSensor', sensor.PollingSensorComponent)
+
+CONFIG_SCHEMA = cv.nameable(sensor.SENSOR_SCHEMA.extend({
+    cv.GenerateID(): cv.declare_variable_id(ADCSensor),
+    cv.Required(CONF_PIN): validate_adc_pin,
+    cv.Optional(CONF_ATTENUATION): cv.All(cv.only_on_esp32, cv.one_of(*ATTENUATION_MODES,
+                                                                      lower=True)),
+
+    cv.Optional(CONF_UPDATE_INTERVAL, default='60s'): cv.update_interval,
+    cv.Optional(CONF_ICON, default=ICON_FLASH): sensor.icon,
+    cv.Optional(CONF_UNIT_OF_MEASUREMENT, default=UNIT_VOLT): sensor.unit_of_measurement,
+    cv.Optional(CONF_ACCURACY_DECIMALS, default=2): sensor.accuracy_decimals,
+}).extend(cv.COMPONENT_SCHEMA))
+
+
+def to_code(config):
+    pin = config[CONF_PIN]
+    if pin == 'VCC':
+        pin = 0
+
+        cg.add_define('USE_ADC_SENSOR_VCC')
+        cg.add_global(cg.global_ns.ADC_MODE(cg.global_ns.ADC_VCC))
+    rhs = ADCSensor.new(config[CONF_NAME], pin, config[CONF_UPDATE_INTERVAL])
+    adc = cg.Pvariable(config[CONF_ID], rhs)
+    yield cg.register_component(adc, config)
+    yield sensor.register_sensor(adc, config)
+
+    if CONF_ATTENUATION in config:
+        cg.add(adc.set_attenuation(ATTENUATION_MODES[config[CONF_ATTENUATION]]))