🏗 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/text_sensor/automation.h

@@ -0,0 +1,31 @@
+#pragma once
+
+#include "esphome/core/component.h"
+#include "esphome/core/automation.h"
+#include "esphome/components/text_sensor/text_sensor.h"
+
+namespace esphome {
+namespace text_sensor {
+
+class TextSensorStateTrigger : public Trigger<std::string> {
+ public:
+  explicit TextSensorStateTrigger(TextSensor *parent) {
+    parent->add_on_state_callback([this](std::string value) { this->trigger(value); });
+  }
+};
+
+template<typename... Ts> class TextSensorPublishAction : public Action<Ts...> {
+ public:
+  TextSensorPublishAction(TextSensor *sensor) : sensor_(sensor) {}
+  TEMPLATABLE_VALUE(std::string, state)
+  void play(Ts... x) override {
+    this->sensor_->publish_state(this->state_.value(x...));
+    this->play_next(x...);
+  }
+
+ protected:
+  TextSensor *sensor_;
+};
+
+}  // namespace text_sensor
+}  // namespace esphome