🏗 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/apds9960/sensor.py

@@ -0,0 +1,32 @@
+import esphome.codegen as cg
+import esphome.config_validation as cv
+from esphome.components import sensor
+from esphome.const import CONF_TYPE, CONF_UNIT_OF_MEASUREMENT, CONF_ACCURACY_DECIMALS, CONF_ICON, \
+    UNIT_PERCENT, ICON_LIGHTBULB
+from . import APDS9960, CONF_APDS9960_ID
+
+DEPENDENCIES = ['apds9960']
+
+TYPES = {
+    'CLEAR': 'set_clear_channel',
+    'RED': 'set_red_channel',
+    'GREEN': 'set_green_channel',
+    'BLUE': 'set_blue_channel',
+    'PROXIMITY': 'set_proximity',
+}
+
+CONFIG_SCHEMA = cv.nameable(sensor.SENSOR_SCHEMA.extend({
+    cv.Required(CONF_TYPE): cv.one_of(*TYPES, upper=True),
+    cv.GenerateID(CONF_APDS9960_ID): cv.use_variable_id(APDS9960),
+
+    cv.Optional(CONF_UNIT_OF_MEASUREMENT, default=UNIT_PERCENT): sensor.unit_of_measurement,
+    cv.Optional(CONF_ACCURACY_DECIMALS, default=1): sensor.accuracy_decimals,
+    cv.Optional(CONF_ICON, default=ICON_LIGHTBULB): sensor.icon,
+}))
+
+
+def to_code(config):
+    hub = yield cg.get_variable(config[CONF_APDS9960_ID])
+    var = yield sensor.new_sensor(config)
+    func = getattr(hub, TYPES[config[CONF_TYPE]])
+    cg.add(func(var))