🏗 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/pulse_width/pulse_width.cpp

@@ -0,0 +1,31 @@
+#include "pulse_width.h"
+#include "esphome/core/log.h"
+
+namespace esphome {
+namespace pulse_width {
+
+static const char *TAG = "pulse_width";
+
+void ICACHE_RAM_ATTR PulseWidthSensorStore::gpio_intr(PulseWidthSensorStore *arg) {
+  const bool new_level = arg->pin_->digital_read();
+  const uint32_t now = micros();
+  if (new_level) {
+    arg->last_rise_ = now;
+  } else {
+    arg->last_width_ = (now - arg->last_rise_);
+  }
+}
+
+void PulseWidthSensor::dump_config() {
+  LOG_SENSOR("", "Pulse Width", this)
+  LOG_UPDATE_INTERVAL(this)
+  LOG_PIN("  Pin: ", this->pin_);
+}
+void PulseWidthSensor::update() {
+  float width = this->store_.get_pulse_width_s();
+  ESP_LOGCONFIG(TAG, "'%s' - Got pulse width %.3f s", this->name_.c_str(), width);
+  this->publish_state(width);
+}
+
+}  // namespace pulse_width
+}  // namespace esphome

esphome/components/pulse_width/pulse_width.h

@@ -0,0 +1,44 @@
+#pragma once
+
+#include "esphome/core/component.h"
+#include "esphome/core/esphal.h"
+#include "esphome/components/sensor/sensor.h"
+
+namespace esphome {
+namespace pulse_width {
+
+/// Store data in a class that doesn't use multiple-inheritance (vtables in flash)
+class PulseWidthSensorStore {
+ public:
+  void setup(GPIOPin *pin) {
+    pin->setup();
+    this->pin_ = pin->to_isr();
+    this->last_rise_ = micros();
+    pin->attach_interrupt(&PulseWidthSensorStore::gpio_intr, this, CHANGE);
+  }
+  static void gpio_intr(PulseWidthSensorStore *arg);
+  uint32_t get_pulse_width_us() const { return this->last_width_; }
+  float get_pulse_width_s() const { return this->last_width_ / 1e6f; }
+
+ protected:
+  ISRInternalGPIOPin *pin_;
+  volatile uint32_t last_width_{0};
+  volatile uint32_t last_rise_{0};
+};
+
+class PulseWidthSensor : public sensor::PollingSensorComponent {
+ public:
+  PulseWidthSensor(const std::string &name, uint32_t update_interval) : PollingSensorComponent(name, update_interval) {}
+  void set_pin(GPIOPin *pin) { pin_ = pin; }
+  void setup() override { this->store_.setup(this->pin_); }
+  void dump_config() override;
+  float get_setup_priority() const override { return setup_priority::DATA; }
+  void update() override;
+
+ protected:
+  PulseWidthSensorStore store_;
+  GPIOPin *pin_;
+};
+
+}  // namespace pulse_width
+}  // namespace esphome

esphome/components/pulse_width/sensor.py

@@ -0,0 +1,26 @@
+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_ID, CONF_NAME, CONF_PIN, CONF_UPDATE_INTERVAL, UNIT_SECOND, \
+    ICON_TIMER
+
+pulse_width_ns = cg.esphome_ns.namespace('pulse_width')
+
+PulseWidthSensor = pulse_width_ns.class_('PulseWidthSensor', sensor.PollingSensorComponent)
+
+CONFIG_SCHEMA = cv.nameable(sensor.sensor_schema(UNIT_SECOND, ICON_TIMER, 3).extend({
+    cv.GenerateID(): cv.declare_variable_id(PulseWidthSensor),
+    cv.Required(CONF_PIN): cv.All(pins.internal_gpio_input_pullup_pin_schema,
+                                  pins.validate_has_interrupt),
+    cv.Optional(CONF_UPDATE_INTERVAL, default='60s'): cv.update_interval,
+}).extend(cv.COMPONENT_SCHEMA))
+
+
+def to_code(config):
+    var = cg.new_Pvariable(config[CONF_ID], config[CONF_NAME], config[CONF_UPDATE_INTERVAL])
+    yield cg.register_component(var, config)
+    yield sensor.register_sensor(var, config)
+
+    pin = yield cg.gpio_pin_expression(config[CONF_PIN])
+    cg.add(var.set_pin(pin))