🏗 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/gpio/switch/gpio_switch.cpp

@@ -0,0 +1,90 @@
+#include "esphome/components/gpio/switch/gpio_switch.h"
+#include "esphome/core/log.h"
+
+namespace esphome {
+namespace gpio {
+
+static const char *TAG = "switch.gpio";
+
+GPIOSwitch::GPIOSwitch(const std::string &name, GPIOPin *pin) : Switch(name), Component(), pin_(pin) {}
+
+float GPIOSwitch::get_setup_priority() const { return setup_priority::HARDWARE; }
+void GPIOSwitch::setup() {
+  ESP_LOGCONFIG(TAG, "Setting up GPIO Switch '%s'...", this->name_.c_str());
+
+  bool initial_state = false;
+  switch (this->restore_mode_) {
+    case GPIO_SWITCH_RESTORE_DEFAULT_OFF:
+      initial_state = this->get_initial_state().value_or(false);
+      break;
+    case GPIO_SWITCH_RESTORE_DEFAULT_ON:
+      initial_state = this->get_initial_state().value_or(true);
+      break;
+    case GPIO_SWITCH_ALWAYS_OFF:
+      initial_state = false;
+      break;
+    case GPIO_SWITCH_ALWAYS_ON:
+      initial_state = true;
+      break;
+  }
+
+  // write state before setup
+  if (initial_state)
+    this->turn_on();
+  else
+    this->turn_off();
+  this->pin_->setup();
+  // write after setup again for other IOs
+  if (initial_state)
+    this->turn_on();
+  else
+    this->turn_off();
+}
+void GPIOSwitch::dump_config() {
+  LOG_SWITCH("", "GPIO Switch", this);
+  LOG_PIN("  Pin: ", this->pin_);
+  const char *restore_mode = "";
+  switch (this->restore_mode_) {
+    case GPIO_SWITCH_RESTORE_DEFAULT_OFF:
+      restore_mode = "Restore (Defaults to OFF)";
+      break;
+    case GPIO_SWITCH_RESTORE_DEFAULT_ON:
+      restore_mode = "Restore (Defaults to ON)";
+      break;
+    case GPIO_SWITCH_ALWAYS_OFF:
+      restore_mode = "Always OFF";
+      break;
+    case GPIO_SWITCH_ALWAYS_ON:
+      restore_mode = "Always ON";
+      break;
+  }
+  ESP_LOGCONFIG(TAG, "  Restore Mode: %s", restore_mode);
+  if (!this->interlock_.empty()) {
+    ESP_LOGCONFIG(TAG, "  Interlocks:");
+    for (auto *lock : this->interlock_) {
+      if (lock == this)
+        continue;
+      ESP_LOGCONFIG(TAG, "    %s", lock->get_name().c_str());
+    }
+  }
+}
+void GPIOSwitch::write_state(bool state) {
+  if (state != this->inverted_) {
+    // Turning ON, check interlocking
+    for (auto *lock : this->interlock_) {
+      if (lock == this)
+        continue;
+
+      if (lock->state)
+        lock->turn_off();
+    }
+  }
+
+  this->pin_->digital_write(state);
+  this->publish_state(state);
+}
+void GPIOSwitch::set_restore_mode(GPIOSwitchRestoreMode restore_mode) { this->restore_mode_ = restore_mode; }
+void GPIOSwitch::set_interlock(const std::vector<Switch *> &interlock) { this->interlock_ = interlock; }
+
+}  // namespace gpio
+}  // namespace esphome