🏗 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/ssd1306_spi/ssd1306_spi.cpp

@@ -0,0 +1,58 @@
+#include "ssd1306_spi.h"
+#include "esphome/core/log.h"
+#include "esphome/core/application.h"
+
+namespace esphome {
+namespace ssd1306_spi {
+
+static const char *TAG = "ssd1306_spi";
+
+bool SPISSD1306::is_device_msb_first() { return true; }
+void SPISSD1306::setup() {
+  ESP_LOGCONFIG(TAG, "Setting up SPI SSD1306...");
+  this->spi_setup();
+  this->dc_pin_->setup();  // OUTPUT
+
+  this->init_reset_();
+  SSD1306::setup();
+}
+void SPISSD1306::dump_config() {
+  LOG_DISPLAY("", "SPI SSD1306", this);
+  ESP_LOGCONFIG(TAG, "  Model: %s", this->model_str_());
+  LOG_PIN("  CS Pin: ", this->cs_);
+  LOG_PIN("  DC Pin: ", this->dc_pin_);
+  LOG_PIN("  Reset Pin: ", this->reset_pin_);
+  ESP_LOGCONFIG(TAG, "  External VCC: %s", YESNO(this->external_vcc_));
+  LOG_UPDATE_INTERVAL(this);
+}
+void SPISSD1306::command(uint8_t value) {
+  this->dc_pin_->digital_write(false);
+  this->enable();
+  this->write_byte(value);
+  this->disable();
+}
+void HOT SPISSD1306::write_display_data() {
+  if (this->is_sh1106_()) {
+    for (uint8_t y = 0; y < this->get_height_internal() / 8; y++) {
+      this->command(0xB0 + y);
+      this->command(0x02);
+      this->command(0x10);
+      this->dc_pin_->digital_write(true);
+      for (uint8_t x = 0; x < this->get_width_internal(); x++) {
+        this->enable();
+        this->write_byte(this->buffer_[x + y * this->get_width_internal()]);
+        this->disable();
+        App.feed_wdt();
+      }
+    }
+  } else {
+    this->dc_pin_->digital_write(true);
+    this->enable();
+    this->write_array(this->buffer_, this->get_buffer_length_());
+    this->disable();
+  }
+}
+bool SPISSD1306::is_device_high_speed() { return true; }
+
+}  // namespace ssd1306_spi
+}  // namespace esphome