🏗 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/core/application.cpp

@@ -0,0 +1,113 @@
+#include "esphome/core/application.h"
+#include "esphome/core/log.h"
+
+#ifdef USE_STATUS_LED
+#include "esphome/components/status_led/status_led.h"
+#endif
+
+namespace esphome {
+
+static const char *TAG = "app";
+
+void Application::register_component_(Component *comp) {
+  if (comp == nullptr) {
+    ESP_LOGW(TAG, "Tried to register null component!");
+    return;
+  }
+
+  for (auto *c : this->components_) {
+    if (comp == c) {
+      ESP_LOGW(TAG, "Component already registered! (%p)", c);
+      return;
+    }
+  }
+  this->components_.push_back(comp);
+}
+void Application::setup() {
+  ESP_LOGI(TAG, "Running through setup()...");
+  ESP_LOGV(TAG, "Sorting components by setup priority...");
+  std::stable_sort(this->components_.begin(), this->components_.end(), [](const Component *a, const Component *b) {
+    return a->get_actual_setup_priority() > b->get_actual_setup_priority();
+  });
+
+  for (uint32_t i = 0; i < this->components_.size(); i++) {
+    Component *component = this->components_[i];
+    if (component->is_failed())
+      continue;
+
+    component->call_setup();
+    if (component->can_proceed())
+      continue;
+
+    std::stable_sort(this->components_.begin(), this->components_.begin() + i + 1,
+                     [](Component *a, Component *b) { return a->get_loop_priority() > b->get_loop_priority(); });
+
+    do {
+      uint32_t new_app_state = STATUS_LED_WARNING;
+      for (uint32_t j = 0; j <= i; j++) {
+        if (!this->components_[j]->is_failed()) {
+          this->components_[j]->call_loop();
+        }
+        new_app_state |= this->components_[j]->get_component_state();
+        this->app_state_ |= new_app_state;
+      }
+      this->app_state_ = new_app_state;
+      yield();
+    } while (!component->can_proceed());
+  }
+
+  ESP_LOGI(TAG, "setup() finished successfully!");
+  this->dump_config();
+}
+void Application::dump_config() {
+  ESP_LOGI(TAG, "esphome-core version " ESPHOME_VERSION " compiled on %s", this->compilation_time_.c_str());
+
+  for (auto component : this->components_) {
+    component->dump_config();
+  }
+}
+
+void ICACHE_RAM_ATTR HOT Application::feed_wdt() {
+  static uint32_t LAST_FEED = 0;
+  uint32_t now = millis();
+  if (now - LAST_FEED > 3) {
+#ifdef ARDUINO_ARCH_ESP8266
+    ESP.wdtFeed();
+#endif
+#ifdef ARDUINO_ARCH_ESP32
+    yield();
+#endif
+    LAST_FEED = now;
+#ifdef USE_STATUS_LED
+    if (status_led::global_status_led != nullptr) {
+      status_led::global_status_led->call_loop();
+    }
+#endif
+  }
+}
+void Application::reboot() {
+  ESP_LOGI(TAG, "Forcing a reboot...");
+  for (auto *comp : this->components_)
+    comp->on_shutdown();
+  ESP.restart();
+  // restart() doesn't always end execution
+  while (true) {
+    yield();
+  }
+}
+void Application::safe_reboot() {
+  ESP_LOGI(TAG, "Rebooting safely...");
+  for (auto *comp : this->components_)
+    comp->on_safe_shutdown();
+  for (auto *comp : this->components_)
+    comp->on_shutdown();
+  ESP.restart();
+  // restart() doesn't always end execution
+  while (true) {
+    yield();
+  }
+}
+
+Application App;
+
+}  // namespace esphome