🏗 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_binary_sensor.cpp

@@ -0,0 +1,54 @@
+#include "mqtt_binary_sensor.h"
+#include "esphome/core/log.h"
+
+#ifdef USE_BINARY_SENSOR
+
+namespace esphome {
+namespace mqtt {
+
+static const char *TAG = "mqtt.binary_sensor";
+
+std::string MQTTBinarySensorComponent::component_type() const { return "binary_sensor"; }
+
+void MQTTBinarySensorComponent::setup() {
+  this->binary_sensor_->add_on_state_callback([this](bool state) { this->publish_state(state); });
+}
+
+void MQTTBinarySensorComponent::dump_config() {
+  ESP_LOGCONFIG(TAG, "MQTT Binary Sensor '%s':", this->binary_sensor_->get_name().c_str());
+  LOG_MQTT_COMPONENT(true, false)
+}
+MQTTBinarySensorComponent::MQTTBinarySensorComponent(binary_sensor::BinarySensor *binary_sensor)
+    : MQTTComponent(), binary_sensor_(binary_sensor) {}
+std::string MQTTBinarySensorComponent::friendly_name() const { return this->binary_sensor_->get_name(); }
+
+void MQTTBinarySensorComponent::send_discovery(JsonObject &root, mqtt::SendDiscoveryConfig &config) {
+  if (!this->binary_sensor_->get_device_class().empty())
+    root["device_class"] = this->binary_sensor_->get_device_class();
+  if (this->is_status_)
+    root["payload_on"] = mqtt::global_mqtt_client->get_availability().payload_available;
+  if (this->is_status_)
+    root["payload_off"] = mqtt::global_mqtt_client->get_availability().payload_not_available;
+  config.command_topic = false;
+}
+bool MQTTBinarySensorComponent::send_initial_state() {
+  if (this->binary_sensor_->has_state()) {
+    return this->publish_state(this->binary_sensor_->state);
+  } else {
+    return true;
+  }
+}
+bool MQTTBinarySensorComponent::is_internal() { return this->binary_sensor_->is_internal(); }
+bool MQTTBinarySensorComponent::publish_state(bool state) {
+  if (this->is_status_)
+    return true;
+
+  const char *state_s = state ? "ON" : "OFF";
+  return this->publish(this->get_state_topic_(), state_s);
+}
+void MQTTBinarySensorComponent::set_is_status(bool status) { this->is_status_ = status; }
+
+}  // namespace mqtt
+}  // namespace esphome
+
+#endif