🏗 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/shutdown/shutdown_switch.cpp

@@ -0,0 +1,30 @@
+#include "shutdown_switch.h"
+#include "esphome/core/log.h"
+#include "esphome/core/application.h"
+
+namespace esphome {
+namespace shutdown {
+
+static const char *TAG = "shutdown.switch";
+
+void ShutdownSwitch::dump_config() { LOG_SWITCH("", "Shutdown Switch", this); }
+void ShutdownSwitch::write_state(bool state) {
+  // Acknowledge
+  this->publish_state(false);
+
+  if (state) {
+    ESP_LOGI(TAG, "Shutting down...");
+    delay(100);  // Let MQTT settle a bit
+
+    App.run_safe_shutdown_hooks();
+#ifdef ARDUINO_ARCH_ESP8266
+    ESP.deepSleep(0);
+#endif
+#ifdef ARDUINO_ARCH_ESP32
+    esp_deep_sleep_start();
+#endif
+  }
+}
+
+}  // namespace shutdown
+}  // namespace esphome

esphome/components/shutdown/shutdown_switch.h

@@ -0,0 +1,20 @@
+#pragma once
+
+#include "esphome/core/component.h"
+#include "esphome/components/switch/switch.h"
+
+namespace esphome {
+namespace shutdown {
+
+class ShutdownSwitch : public switch_::Switch, public Component {
+ public:
+  explicit ShutdownSwitch(const std::string &name) : switch_::Switch(name) {}
+
+  void dump_config() override;
+
+ protected:
+  void write_state(bool state) override;
+};
+
+}  // namespace shutdown
+}  // namespace esphome

esphome/components/shutdown/switch.py

@@ -0,0 +1,21 @@
+from esphome.components import switch
+import esphome.config_validation as cv
+import esphome.codegen as cg
+from esphome.const import CONF_ID, CONF_INVERTED, CONF_NAME, CONF_ICON, ICON_POWER
+
+shutdown_ns = cg.esphome_ns.namespace('shutdown')
+ShutdownSwitch = shutdown_ns.class_('ShutdownSwitch', switch.Switch, cg.Component)
+
+CONFIG_SCHEMA = cv.nameable(switch.SWITCH_SCHEMA.extend({
+    cv.GenerateID(): cv.declare_variable_id(ShutdownSwitch),
+
+    cv.Optional(CONF_INVERTED): cv.invalid("Shutdown switches do not support inverted mode!"),
+
+    cv.Optional(CONF_ICON, default=ICON_POWER): switch.icon
+}).extend(cv.COMPONENT_SCHEMA))
+
+
+def to_code(config):
+    var = cg.new_Pvariable(config[CONF_ID], config[CONF_NAME])
+    yield cg.register_component(var, config)
+    yield switch.register_switch(var, config)