🏗 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/esp8266_pwm/esp8266_pwm.cpp

@@ -0,0 +1,49 @@
+#include "esp8266_pwm.h"
+#include "esphome/core/log.h"
+#include "esphome/core/helpers.h"
+
+#ifdef ARDUINO_ESP8266_RELEASE_2_3_0
+#error ESP8266 PWM requires at least arduino_core_version 2.4.0
+#endif
+
+#include <core_esp8266_waveform.h>
+
+namespace esphome {
+namespace esp8266_pwm {
+
+static const char *TAG = "something.something";
+
+void ESP8266PWM::setup() {
+  ESP_LOGCONFIG(TAG, "Setting up ESP8266 PWM Output...");
+  this->pin_->setup();
+  this->turn_off();
+}
+void ESP8266PWM::dump_config() {
+  ESP_LOGCONFIG(TAG, "ESP8266 PWM:");
+  LOG_PIN("  Pin: ", this->pin_);
+  ESP_LOGCONFIG(TAG, "  Frequency: %.1f Hz", this->frequency_);
+  LOG_FLOAT_OUTPUT(this);
+}
+void HOT ESP8266PWM::write_state(float state) {
+  // Also check pin inversion
+  if (this->pin_->is_inverted()) {
+    state = 1.0f - state;
+  }
+
+  auto total_time_us = static_cast<uint32_t>(roundf(1e6f / this->frequency_));
+  auto duty_on = static_cast<uint32_t>(roundf(total_time_us * state));
+  uint32_t duty_off = total_time_us - duty_on;
+
+  if (duty_on == 0) {
+    stopWaveform(this->pin_->get_pin());
+    this->pin_->digital_write(this->pin_->is_inverted());
+  } else if (duty_off == 0) {
+    stopWaveform(this->pin_->get_pin());
+    this->pin_->digital_write(!this->pin_->is_inverted());
+  } else {
+    startWaveform(this->pin_->get_pin(), duty_on, duty_off, 0);
+  }
+}
+
+}  // namespace esp8266_pwm
+}  // namespace esphome