🏗 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/sensor/sensor.cpp

@@ -0,0 +1,118 @@
+#include "esphome/components/sensor/sensor.h"
+#include "esphome/core/log.h"
+
+namespace esphome {
+namespace sensor {
+
+static const char *TAG = "sensor";
+
+void Sensor::publish_state(float state) {
+  this->raw_state = state;
+  this->raw_callback_.call(state);
+
+  ESP_LOGV(TAG, "'%s': Received new state %f", this->name_.c_str(), state);
+
+  if (this->filter_list_ == nullptr) {
+    this->internal_send_state_to_frontend(state);
+  } else {
+    this->filter_list_->input(state);
+  }
+}
+void Sensor::push_new_value(float state) { this->publish_state(state); }
+std::string Sensor::unit_of_measurement() { return ""; }
+std::string Sensor::icon() { return ""; }
+uint32_t Sensor::update_interval() { return 0; }
+int8_t Sensor::accuracy_decimals() { return 0; }
+Sensor::Sensor(const std::string &name) : Nameable(name), state(NAN), raw_state(NAN) {}
+Sensor::Sensor() : Sensor("") {}
+
+void Sensor::set_unit_of_measurement(const std::string &unit_of_measurement) {
+  this->unit_of_measurement_ = unit_of_measurement;
+}
+void Sensor::set_icon(const std::string &icon) { this->icon_ = icon; }
+void Sensor::set_accuracy_decimals(int8_t accuracy_decimals) { this->accuracy_decimals_ = accuracy_decimals; }
+void Sensor::add_on_state_callback(std::function<void(float)> &&callback) { this->callback_.add(std::move(callback)); }
+void Sensor::add_on_raw_state_callback(std::function<void(float)> &&callback) {
+  this->raw_callback_.add(std::move(callback));
+}
+std::string Sensor::get_icon() {
+  if (this->icon_.has_value())
+    return *this->icon_;
+  return this->icon();
+}
+std::string Sensor::get_unit_of_measurement() {
+  if (this->unit_of_measurement_.has_value())
+    return *this->unit_of_measurement_;
+  return this->unit_of_measurement();
+}
+int8_t Sensor::get_accuracy_decimals() {
+  if (this->accuracy_decimals_.has_value())
+    return *this->accuracy_decimals_;
+  return this->accuracy_decimals();
+}
+void Sensor::add_filter(Filter *filter) {
+  // inefficient, but only happens once on every sensor setup and nobody's going to have massive amounts of
+  // filters
+  ESP_LOGVV(TAG, "Sensor(%p)::add_filter(%p)", this, filter);
+  if (this->filter_list_ == nullptr) {
+    this->filter_list_ = filter;
+  } else {
+    Filter *last_filter = this->filter_list_;
+    while (last_filter->next_ != nullptr)
+      last_filter = last_filter->next_;
+    last_filter->initialize(this, filter);
+  }
+  filter->initialize(this, nullptr);
+}
+void Sensor::add_filters(const std::vector<Filter *> &filters) {
+  for (Filter *filter : filters) {
+    this->add_filter(filter);
+  }
+}
+void Sensor::set_filters(const std::vector<Filter *> &filters) {
+  this->clear_filters();
+  this->add_filters(filters);
+}
+void Sensor::clear_filters() {
+  if (this->filter_list_ != nullptr) {
+    ESP_LOGVV(TAG, "Sensor(%p)::clear_filters()", this);
+  }
+  this->filter_list_ = nullptr;
+}
+float Sensor::get_value() const { return this->state; }
+float Sensor::get_state() const { return this->state; }
+float Sensor::get_raw_value() const { return this->raw_state; }
+float Sensor::get_raw_state() const { return this->raw_state; }
+std::string Sensor::unique_id() { return ""; }
+
+void Sensor::internal_send_state_to_frontend(float state) {
+  this->has_state_ = true;
+  this->state = state;
+  if (this->filter_list_ != nullptr) {
+    ESP_LOGD(TAG, "'%s': Sending state %.5f %s with %d decimals of accuracy", this->get_name().c_str(), state,
+             this->get_unit_of_measurement().c_str(), this->get_accuracy_decimals());
+  }
+  this->callback_.call(state);
+}
+bool Sensor::has_state() const { return this->has_state_; }
+uint32_t Sensor::calculate_expected_filter_update_interval() {
+  uint32_t interval = this->update_interval();
+  if (interval == 4294967295UL)
+    // update_interval: never
+    return 0;
+
+  if (this->filter_list_ == nullptr) {
+    return interval;
+  }
+
+  return this->filter_list_->calculate_remaining_interval(interval);
+}
+uint32_t Sensor::hash_base() { return 2455723294UL; }
+
+PollingSensorComponent::PollingSensorComponent(const std::string &name, uint32_t update_interval)
+    : PollingComponent(update_interval), Sensor(name) {}
+
+uint32_t PollingSensorComponent::update_interval() { return this->get_update_interval(); }
+
+}  // namespace sensor
+}  // namespace esphome