🏗 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_i2c/display.py

@@ -0,0 +1,21 @@
+import esphome.codegen as cg
+import esphome.config_validation as cv
+from esphome.components import ssd1306_base, i2c
+from esphome.const import CONF_ID, CONF_LAMBDA, CONF_PAGES
+
+AUTO_LOAD = ['ssd1306_base']
+DEPENDENCIES = ['i2c']
+
+ssd1306_i2c = cg.esphome_ns.namespace('ssd1306_i2c')
+I2CSSD1306 = ssd1306_i2c.class_('I2CSSD1306', ssd1306_base.SSD1306, i2c.I2CDevice)
+
+CONFIG_SCHEMA = cv.All(ssd1306_base.SSD1306_SCHEMA.extend({
+    cv.GenerateID(): cv.declare_variable_id(I2CSSD1306),
+}).extend(cv.COMPONENT_SCHEMA).extend(i2c.i2c_device_schema(0x3C)),
+                       cv.has_at_most_one_key(CONF_PAGES, CONF_LAMBDA))
+
+
+def to_code(config):
+    var = cg.new_Pvariable(config[CONF_ID])
+    yield ssd1306_base.setup_ssd1036(var, config)
+    yield i2c.register_i2c_device(var, config)

esphome/components/ssd1306_i2c/ssd1306_i2c.cpp

@@ -0,0 +1,61 @@
+#include "ssd1306_i2c.h"
+#include "esphome/core/log.h"
+
+namespace esphome {
+namespace ssd1306_i2c {
+
+static const char *TAG = "ssd1306_i2c";
+
+void I2CSSD1306::setup() {
+  ESP_LOGCONFIG(TAG, "Setting up I2C SSD1306...");
+  this->init_reset_();
+
+  this->parent_->raw_begin_transmission(this->address_);
+  if (!this->parent_->raw_end_transmission(this->address_)) {
+    this->error_code_ = COMMUNICATION_FAILED;
+    this->mark_failed();
+    return;
+  }
+
+  SSD1306::setup();
+}
+void I2CSSD1306::dump_config() {
+  LOG_DISPLAY("", "I2C SSD1306", this);
+  LOG_I2C_DEVICE(this);
+  ESP_LOGCONFIG(TAG, "  Model: %s", this->model_str_());
+  LOG_PIN("  Reset Pin: ", this->reset_pin_);
+  ESP_LOGCONFIG(TAG, "  External VCC: %s", YESNO(this->external_vcc_));
+  LOG_UPDATE_INTERVAL(this);
+
+  if (this->error_code_ == COMMUNICATION_FAILED) {
+    ESP_LOGE(TAG, "Communication with SSD1306 failed!");
+  }
+}
+void I2CSSD1306::command(uint8_t value) { this->write_byte(0x00, value); }
+void HOT I2CSSD1306::write_display_data() {
+  if (this->is_sh1106_()) {
+    uint32_t i = 0;
+    for (uint8_t page = 0; page < this->get_height_internal() / 8; page++) {
+      this->command(0xB0 + page);  // row
+      this->command(0x02);         // lower column
+      this->command(0x10);         // higher column
+
+      for (uint8_t x = 0; x < this->get_width_internal() / 16; x++) {
+        uint8_t data[16];
+        for (uint8_t &j : data)
+          j = this->buffer_[i++];
+        this->write_bytes(0x40, data, sizeof(data));
+      }
+    }
+  } else {
+    for (uint32_t i = 0; i < this->get_buffer_length_();) {
+      uint8_t data[16];
+      for (uint8_t &j : data)
+        j = this->buffer_[i++];
+      this->write_bytes(0x40, data, sizeof(data));
+    }
+  }
+}
+
+}  // namespace ssd1306_i2c
+}  // namespace esphome

esphome/components/ssd1306_i2c/ssd1306_i2c.h

@@ -0,0 +1,25 @@
+#pragma once
+
+#include "esphome/core/component.h"
+#include "esphome/components/ssd1306_base/ssd1306_base.h"
+#include "esphome/components/i2c/i2c.h"
+
+namespace esphome {
+namespace ssd1306_i2c {
+
+class I2CSSD1306 : public ssd1306_base::SSD1306, public i2c::I2CDevice {
+ public:
+  I2CSSD1306() = default;
+
+  void setup() override;
+  void dump_config() override;
+
+ protected:
+  void command(uint8_t value) override;
+  void write_display_data() override;
+
+  enum ErrorCode { NONE = 0, COMMUNICATION_FAILED } error_code_{NONE};
+};
+
+}  // namespace ssd1306_i2c
+}  // namespace esphome