🏗 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/dallas/sensor.py

@@ -0,0 +1,34 @@
+import esphome.codegen as cg
+import esphome.config_validation as cv
+from esphome.components import sensor
+from esphome.const import CONF_ADDRESS, CONF_DALLAS_ID, CONF_INDEX, CONF_NAME, \
+    CONF_RESOLUTION, CONF_UNIT_OF_MEASUREMENT, UNIT_CELSIUS, CONF_ICON, ICON_THERMOMETER, \
+    CONF_ACCURACY_DECIMALS, CONF_ID
+from . import DallasComponent, dallas_ns
+
+DallasTemperatureSensor = dallas_ns.class_('DallasTemperatureSensor', sensor.Sensor)
+
+CONFIG_SCHEMA = cv.nameable(sensor.SENSOR_SCHEMA.extend({
+    cv.GenerateID(): cv.declare_variable_id(DallasTemperatureSensor),
+    cv.GenerateID(CONF_DALLAS_ID): cv.use_variable_id(DallasComponent),
+
+    cv.Optional(CONF_ADDRESS): cv.hex_int,
+    cv.Optional(CONF_INDEX): cv.positive_int,
+    cv.Optional(CONF_RESOLUTION, default=12): cv.All(cv.int_, cv.Range(min=9, max=12)),
+
+    cv.Optional(CONF_UNIT_OF_MEASUREMENT, default=UNIT_CELSIUS): sensor.unit_of_measurement,
+    cv.Optional(CONF_ICON, default=ICON_THERMOMETER): sensor.icon,
+    cv.Optional(CONF_ACCURACY_DECIMALS, default=1): sensor.accuracy_decimals,
+}), cv.has_exactly_one_key(CONF_ADDRESS, CONF_INDEX))
+
+
+def to_code(config):
+    hub = yield cg.get_variable(config[CONF_DALLAS_ID])
+    if CONF_ADDRESS in config:
+        address = config[CONF_ADDRESS]
+        rhs = hub.Pget_sensor_by_address(config[CONF_NAME], address, config.get(CONF_RESOLUTION))
+    else:
+        rhs = hub.Pget_sensor_by_index(config[CONF_NAME], config[CONF_INDEX],
+                                       config.get(CONF_RESOLUTION))
+    var = cg.Pvariable(config[CONF_ID], rhs)
+    yield sensor.register_sensor(var, config)