🏗 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/mqtt/mqtt_fan.cpp

@@ -0,0 +1,124 @@
+#include "mqtt_fan.h"
+#include "esphome/core/log.h"
+
+#ifdef USE_FAN
+
+namespace esphome {
+namespace mqtt {
+
+static const char *TAG = "mqtt.fan";
+
+using namespace esphome::fan;
+
+MQTTFanComponent::MQTTFanComponent(FanState *state) : MQTTComponent(), state_(state) {}
+
+FanState *MQTTFanComponent::get_state() const { return this->state_; }
+std::string MQTTFanComponent::component_type() const { return "fan"; }
+void MQTTFanComponent::setup() {
+  this->subscribe(this->get_command_topic_(), [this](const std::string &topic, const std::string &payload) {
+    auto val = parse_on_off(payload.c_str());
+    switch (val) {
+      case PARSE_ON:
+        ESP_LOGD(TAG, "'%s' Turning Fan ON.", this->friendly_name().c_str());
+        this->state_->turn_on().perform();
+        break;
+      case PARSE_OFF:
+        ESP_LOGD(TAG, "'%s' Turning Fan OFF.", this->friendly_name().c_str());
+        this->state_->turn_off().perform();
+        break;
+      case PARSE_TOGGLE:
+        ESP_LOGD(TAG, "'%s' Toggling Fan.", this->friendly_name().c_str());
+        this->state_->toggle().perform();
+        break;
+      case PARSE_NONE:
+      default:
+        ESP_LOGW(TAG, "Unknown state payload %s", payload.c_str());
+        this->status_momentary_warning("state", 5000);
+        break;
+    }
+  });
+
+  if (this->state_->get_traits().supports_oscillation()) {
+    this->subscribe(this->get_oscillation_command_topic(),
+                    [this](const std::string &topic, const std::string &payload) {
+                      auto val = parse_on_off(payload.c_str(), "oscillate_on", "oscillate_off");
+                      switch (val) {
+                        case PARSE_ON:
+                          ESP_LOGD(TAG, "'%s': Setting oscillating ON", this->friendly_name().c_str());
+                          this->state_->make_call().set_oscillating(true).perform();
+                          break;
+                        case PARSE_OFF:
+                          ESP_LOGD(TAG, "'%s': Setting oscillating OFF", this->friendly_name().c_str());
+                          this->state_->make_call().set_oscillating(false).perform();
+                          break;
+                        case PARSE_TOGGLE:
+                          this->state_->make_call().set_oscillating(!this->state_->oscillating).perform();
+                          break;
+                        case PARSE_NONE:
+                          ESP_LOGW(TAG, "Unknown Oscillation Payload %s", payload.c_str());
+                          this->status_momentary_warning("oscillation", 5000);
+                          break;
+                      }
+                    });
+  }
+
+  if (this->state_->get_traits().supports_speed()) {
+    this->subscribe(this->get_speed_command_topic(), [this](const std::string &topic, const std::string &payload) {
+      this->state_->make_call().set_speed(payload.c_str()).perform();
+    });
+  }
+
+  auto f = std::bind(&MQTTFanComponent::publish_state, this);
+  this->state_->add_on_state_callback([this, f]() { this->defer("send", f); });
+}
+bool MQTTFanComponent::send_initial_state() { return this->publish_state(); }
+std::string MQTTFanComponent::friendly_name() const { return this->state_->get_name(); }
+void MQTTFanComponent::send_discovery(JsonObject &root, mqtt::SendDiscoveryConfig &config) {
+  if (this->state_->get_traits().supports_oscillation()) {
+    root["oscillation_command_topic"] = this->get_oscillation_command_topic();
+    root["oscillation_state_topic"] = this->get_oscillation_state_topic();
+  }
+  if (this->state_->get_traits().supports_speed()) {
+    root["speed_command_topic"] = this->get_speed_command_topic();
+    root["speed_state_topic"] = this->get_speed_state_topic();
+  }
+}
+bool MQTTFanComponent::is_internal() { return this->state_->is_internal(); }
+bool MQTTFanComponent::publish_state() {
+  const char *state_s = this->state_->state ? "ON" : "OFF";
+  ESP_LOGD(TAG, "'%s' Sending state %s.", this->state_->get_name().c_str(), state_s);
+  this->publish(this->get_state_topic_(), state_s);
+  bool failed = false;
+  if (this->state_->get_traits().supports_oscillation()) {
+    bool success = this->publish(this->get_oscillation_state_topic(),
+                                 this->state_->oscillating ? "oscillate_on" : "oscillate_off");
+    failed = failed || !success;
+  }
+  if (this->state_->get_traits().supports_speed()) {
+    const char *payload;
+    switch (this->state_->speed) {
+      case FAN_SPEED_LOW: {
+        payload = "low";
+        break;
+      }
+      case FAN_SPEED_MEDIUM: {
+        payload = "medium";
+        break;
+      }
+      default:
+      case FAN_SPEED_HIGH: {
+        payload = "high";
+        break;
+      }
+    }
+    bool success = this->publish(this->get_speed_state_topic(), payload);
+    failed = failed || !success;
+  }
+
+  return !failed;
+}
+
+}  // namespace mqtt
+}  // namespace esphome
+
+#endif