🏗 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/lcd_gpio/gpio_lcd_display.h

@@ -0,0 +1,48 @@
+#pragma once
+
+#include "esphome/core/esphal.h"
+#include "esphome/components/lcd_base/lcd_display.h"
+
+namespace esphome {
+namespace lcd_gpio {
+
+class GPIOLCDDisplay : public lcd_base::LCDDisplay {
+ public:
+  GPIOLCDDisplay(uint32_t update_interval) : LCDDisplay(update_interval) {}
+
+  void setup() override;
+  void set_data_pins(GPIOPin *d0, GPIOPin *d1, GPIOPin *d2, GPIOPin *d3) {
+    this->data_pins_[0] = d0;
+    this->data_pins_[1] = d1;
+    this->data_pins_[2] = d2;
+    this->data_pins_[3] = d3;
+  }
+  void set_data_pins(GPIOPin *d0, GPIOPin *d1, GPIOPin *d2, GPIOPin *d3, GPIOPin *d4, GPIOPin *d5, GPIOPin *d6,
+                     GPIOPin *d7) {
+    this->data_pins_[0] = d0;
+    this->data_pins_[1] = d1;
+    this->data_pins_[2] = d2;
+    this->data_pins_[3] = d3;
+    this->data_pins_[4] = d4;
+    this->data_pins_[5] = d5;
+    this->data_pins_[6] = d6;
+    this->data_pins_[7] = d7;
+  }
+  void set_enable_pin(GPIOPin *enable) { this->enable_pin_ = enable; }
+  void set_rs_pin(GPIOPin *rs) { this->rs_pin_ = rs; }
+  void set_rw_pin(GPIOPin *rw) { this->rw_pin_ = rw; }
+  void dump_config() override;
+
+ protected:
+  bool is_four_bit_mode() override { return this->data_pins_[4] == nullptr; }
+  void write_n_bits(uint8_t value, uint8_t n) override;
+  void send(uint8_t value, bool rs) override;
+
+  GPIOPin *rs_pin_{nullptr};
+  GPIOPin *rw_pin_{nullptr};
+  GPIOPin *enable_pin_{nullptr};
+  GPIOPin *data_pins_[8]{nullptr, nullptr, nullptr, nullptr, nullptr, nullptr, nullptr, nullptr};
+};
+
+}  // namespace lcd_gpio
+}  // namespace esphome