🏗 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/power_supply/power_supply.h

@@ -0,0 +1,41 @@
+#pragma once
+
+#include "esphome/core/component.h"
+#include "esphome/core/esphal.h"
+
+namespace esphome {
+namespace power_supply {
+
+class PowerSupply : public Component {
+ public:
+  explicit PowerSupply(GPIOPin *pin, uint32_t enable_time, uint32_t keep_on_time);
+
+  /// Is this power supply currently on?
+  bool is_enabled() const;
+
+  /// Request high power mode. Use unrequest_high_power() to remove this request.
+  void request_high_power();
+
+  /// Un-request high power mode.
+  void unrequest_high_power();
+
+  // ========== INTERNAL METHODS ==========
+  // (In most use cases you won't need these)
+  /// Register callbacks.
+  void setup() override;
+  void dump_config() override;
+  /// Hardware setup priority (+1).
+  float get_setup_priority() const override;
+
+  void on_shutdown() override;
+
+ protected:
+  GPIOPin *pin_;
+  bool enabled_{false};
+  uint32_t enable_time_;
+  uint32_t keep_on_time_;
+  int16_t active_requests_{0};  // use signed integer to make catching negative requests easier.
+};
+
+}  // namespace power_supply
+}  // namespace esphome