🏗 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/dht/sensor.py

@@ -0,0 +1,50 @@
+from esphome.components import sensor
+import esphome.config_validation as cv
+import esphome.codegen as cg
+from esphome.const import CONF_HUMIDITY, CONF_ID, CONF_MODEL, CONF_NAME, \
+    CONF_PIN, CONF_TEMPERATURE, CONF_UPDATE_INTERVAL, CONF_ACCURACY_DECIMALS, CONF_ICON, \
+    ICON_THERMOMETER, CONF_UNIT_OF_MEASUREMENT, UNIT_CELSIUS, ICON_WATER_PERCENT, UNIT_PERCENT
+from esphome.cpp_helpers import gpio_pin_expression
+from esphome.pins import gpio_input_pullup_pin_schema
+
+dht_ns = cg.esphome_ns.namespace('dht')
+DHTModel = dht_ns.enum('DHTModel')
+DHT_MODELS = {
+    'AUTO_DETECT': DHTModel.DHT_MODEL_AUTO_DETECT,
+    'DHT11': DHTModel.DHT_MODEL_DHT11,
+    'DHT22': DHTModel.DHT_MODEL_DHT22,
+    'AM2302': DHTModel.DHT_MODEL_AM2302,
+    'RHT03': DHTModel.DHT_MODEL_RHT03,
+    'SI7021': DHTModel.DHT_MODEL_SI7021,
+}
+DHT = dht_ns.class_('DHT', cg.PollingComponent)
+
+CONFIG_SCHEMA = cv.Schema({
+    cv.GenerateID(): cv.declare_variable_id(DHT),
+    cv.Required(CONF_PIN): gpio_input_pullup_pin_schema,
+    cv.Required(CONF_TEMPERATURE): cv.nameable(sensor.SENSOR_SCHEMA.extend({
+        cv.Optional(CONF_ACCURACY_DECIMALS, default=1): sensor.accuracy_decimals,
+        cv.Optional(CONF_ICON, default=ICON_THERMOMETER): sensor.icon,
+        cv.Optional(CONF_UNIT_OF_MEASUREMENT, default=UNIT_CELSIUS): sensor.unit_of_measurement,
+    })),
+    cv.Required(CONF_HUMIDITY): cv.nameable(sensor.SENSOR_SCHEMA.extend({
+        cv.Optional(CONF_ACCURACY_DECIMALS, default=0): sensor.accuracy_decimals,
+        cv.Optional(CONF_ICON, default=ICON_WATER_PERCENT): sensor.icon,
+        cv.Optional(CONF_UNIT_OF_MEASUREMENT, default=UNIT_PERCENT): sensor.unit_of_measurement,
+    })),
+    cv.Optional(CONF_MODEL, default='auto detect'): cv.one_of(*DHT_MODELS, upper=True, space='_'),
+    cv.Optional(CONF_UPDATE_INTERVAL, default='60s'): cv.update_interval,
+}).extend(cv.COMPONENT_SCHEMA)
+
+
+def to_code(config):
+    pin = yield gpio_pin_expression(config[CONF_PIN])
+    rhs = DHT.new(config[CONF_TEMPERATURE][CONF_NAME],
+                  config[CONF_HUMIDITY][CONF_NAME],
+                  pin, config[CONF_UPDATE_INTERVAL])
+    dht = cg.Pvariable(config[CONF_ID], rhs)
+    yield cg.register_component(dht, config)
+    yield sensor.register_sensor(dht.Pget_temperature_sensor(), config[CONF_TEMPERATURE])
+    yield sensor.register_sensor(dht.Pget_humidity_sensor(), config[CONF_HUMIDITY])
+
+    cg.add(dht.set_dht_model(DHT_MODELS[config[CONF_MODEL]]))