🏗 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/status_led/__init__.py

@@ -0,0 +1,23 @@
+from esphome import pins
+import esphome.config_validation as cv
+import esphome.codegen as cg
+from esphome.const import CONF_ID, CONF_PIN
+from esphome.core import coroutine_with_priority
+
+status_led_ns = cg.esphome_ns.namespace('status_led')
+StatusLED = status_led_ns.class_('StatusLED', cg.Component)
+
+CONFIG_SCHEMA = cv.Schema({
+    cv.GenerateID(): cv.declare_variable_id(StatusLED),
+    cv.Required(CONF_PIN): pins.gpio_output_pin_schema,
+}).extend(cv.COMPONENT_SCHEMA)
+
+
+@coroutine_with_priority(80.0)
+def to_code(config):
+    pin = yield cg.gpio_pin_expression(config[CONF_PIN])
+    rhs = StatusLED.new(pin)
+    var = cg.Pvariable(config[CONF_ID], rhs)
+    yield cg.register_component(var, config)
+    cg.add(var.pre_setup())
+    cg.add_define('USE_STATUS_LED')

esphome/components/status_led/status_led.cpp

@@ -0,0 +1,35 @@
+#include "status_led.h"
+#include "esphome/core/log.h"
+#include "esphome/core/application.h"
+
+namespace esphome {
+namespace status_led {
+
+static const char *TAG = "status_led";
+
+StatusLED *global_status_led = nullptr;
+
+StatusLED::StatusLED(GPIOPin *pin) : pin_(pin) { global_status_led = this; }
+void StatusLED::pre_setup() {
+  ESP_LOGCONFIG(TAG, "Setting up Status LED...");
+  this->pin_->setup();
+  this->pin_->digital_write(false);
+}
+void StatusLED::dump_config() {
+  ESP_LOGCONFIG(TAG, "Status LED:");
+  LOG_PIN("  Pin: ", this->pin_);
+}
+void StatusLED::loop() {
+  if ((App.get_app_state() & STATUS_LED_ERROR) != 0u) {
+    this->pin_->digital_write(millis() % 250u < 150u);
+  } else if ((App.get_app_state() & STATUS_LED_WARNING) != 0u) {
+    this->pin_->digital_write(millis() % 1500u < 250u);
+  } else {
+    this->pin_->digital_write(false);
+  }
+}
+float StatusLED::get_setup_priority() const { return setup_priority::HARDWARE; }
+float StatusLED::get_loop_priority() const { return 50.0f; }
+
+}  // namespace status_led
+}  // namespace esphome

esphome/components/status_led/status_led.h

@@ -0,0 +1,26 @@
+#pragma once
+
+#include "esphome/core/component.h"
+#include "esphome/core/esphal.h"
+
+namespace esphome {
+namespace status_led {
+
+class StatusLED : public Component {
+ public:
+  explicit StatusLED(GPIOPin *pin);
+
+  void pre_setup();
+  void dump_config() override;
+  void loop() override;
+  float get_setup_priority() const override;
+  float get_loop_priority() const override;
+
+ protected:
+  GPIOPin *pin_;
+};
+
+extern StatusLED *global_status_led;
+
+}  // namespace status_led
+}  // namespace esphome