🏗 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/ultrasonic/ultrasonic_sensor.cpp

@@ -0,0 +1,56 @@
+#include "ultrasonic_sensor.h"
+#include "esphome/core/log.h"
+
+namespace esphome {
+namespace ultrasonic {
+
+static const char *TAG = "ultrasonic.sensor";
+
+UltrasonicSensorComponent::UltrasonicSensorComponent(const std::string &name, GPIOPin *trigger_pin, GPIOPin *echo_pin,
+                                                     uint32_t update_interval)
+    : PollingSensorComponent(name, update_interval), trigger_pin_(trigger_pin), echo_pin_(echo_pin) {}
+void UltrasonicSensorComponent::setup() {
+  ESP_LOGCONFIG(TAG, "Setting up Ultrasonic Sensor...");
+  this->trigger_pin_->setup();
+  this->trigger_pin_->digital_write(false);
+  this->echo_pin_->setup();
+}
+void UltrasonicSensorComponent::update() {
+  this->trigger_pin_->digital_write(true);
+  delayMicroseconds(this->pulse_time_us_);
+  this->trigger_pin_->digital_write(false);
+
+  uint32_t time = pulseIn(this->echo_pin_->get_pin(), uint8_t(!this->echo_pin_->is_inverted()), this->timeout_us_);
+
+  ESP_LOGV(TAG, "Echo took %uµs", time);
+
+  if (time == 0) {
+    ESP_LOGD(TAG, "'%s' - Distance measurement timed out!", this->name_.c_str());
+    this->publish_state(NAN);
+  } else {
+    float result = UltrasonicSensorComponent::us_to_m(time);
+    this->publish_state(result);
+    ESP_LOGD(TAG, "'%s' - Got distance: %.2f m", this->name_.c_str(), result);
+    this->publish_state(result);
+  }
+}
+void UltrasonicSensorComponent::dump_config() {
+  LOG_SENSOR("", "Ultrasonic Sensor", this);
+  LOG_PIN("  Echo Pin: ", this->echo_pin_);
+  LOG_PIN("  Trigger Pin: ", this->trigger_pin_);
+  ESP_LOGCONFIG(TAG, "  Pulse time: %u µs", this->pulse_time_us_);
+  ESP_LOGCONFIG(TAG, "  Timeout: %u µs", this->timeout_us_);
+  LOG_UPDATE_INTERVAL(this);
+}
+float UltrasonicSensorComponent::us_to_m(uint32_t us) {
+  const float speed_sound_m_per_s = 343.0f;
+  const float time_s = us / 1e6f;
+  const float total_dist = time_s * speed_sound_m_per_s;
+  return total_dist / 2.0f;
+}
+float UltrasonicSensorComponent::get_setup_priority() const { return setup_priority::DATA; }
+void UltrasonicSensorComponent::set_pulse_time_us(uint32_t pulse_time_us) { this->pulse_time_us_ = pulse_time_us; }
+void UltrasonicSensorComponent::set_timeout_us(uint32_t timeout_us) { this->timeout_us_ = timeout_us; }
+
+}  // namespace ultrasonic
+}  // namespace esphome