🏗 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/ina3221/sensor.py

@@ -0,0 +1,58 @@
+# coding=utf-8
+import esphome.codegen as cg
+import esphome.config_validation as cv
+from esphome.components import i2c, sensor
+from esphome.const import CONF_BUS_VOLTAGE, CONF_CURRENT, CONF_ID, CONF_POWER, \
+    CONF_SHUNT_RESISTANCE, CONF_SHUNT_VOLTAGE, CONF_UPDATE_INTERVAL, ICON_FLASH, \
+    UNIT_VOLT, UNIT_AMPERE, UNIT_WATT
+
+DEPENDENCIES = ['i2c']
+
+CONF_CHANNEL_1 = 'channel_1'
+CONF_CHANNEL_2 = 'channel_2'
+CONF_CHANNEL_3 = 'channel_3'
+
+ina3221_ns = cg.esphome_ns.namespace('ina3221')
+INA3221Component = ina3221_ns.class_('INA3221Component', cg.PollingComponent, i2c.I2CDevice)
+
+INA3221_CHANNEL_SCHEMA = cv.Schema({
+    cv.Optional(CONF_BUS_VOLTAGE): cv.nameable(sensor.sensor_schema(UNIT_VOLT, ICON_FLASH, 2)),
+    cv.Optional(CONF_SHUNT_VOLTAGE): cv.nameable(sensor.sensor_schema(UNIT_VOLT, ICON_FLASH, 2)),
+    cv.Optional(CONF_CURRENT): cv.nameable(sensor.sensor_schema(UNIT_AMPERE, ICON_FLASH, 2)),
+    cv.Optional(CONF_POWER): cv.nameable(sensor.sensor_schema(UNIT_WATT, ICON_FLASH, 2)),
+    cv.Optional(CONF_SHUNT_RESISTANCE, default=0.1): cv.All(cv.resistance,
+                                                            cv.Range(min=0.0, max=32.0)),
+})
+
+CONFIG_SCHEMA = cv.Schema({
+    cv.GenerateID(): cv.declare_variable_id(INA3221Component),
+    cv.Optional(CONF_CHANNEL_1): INA3221_CHANNEL_SCHEMA,
+    cv.Optional(CONF_CHANNEL_2): INA3221_CHANNEL_SCHEMA,
+    cv.Optional(CONF_CHANNEL_3): INA3221_CHANNEL_SCHEMA,
+    cv.Optional(CONF_UPDATE_INTERVAL, default='60s'): cv.update_interval,
+}).extend(cv.COMPONENT_SCHEMA).extend(i2c.i2c_device_schema(0x40))
+
+
+def to_code(config):
+    var = cg.new_Pvariable(config[CONF_ID], config[CONF_UPDATE_INTERVAL])
+    yield cg.register_component(var, config)
+    yield i2c.register_i2c_device(var, config)
+
+    for i, channel in enumerate([CONF_CHANNEL_1, CONF_CHANNEL_2, CONF_CHANNEL_3]):
+        if channel not in config:
+            continue
+        conf = config[channel]
+        if CONF_SHUNT_RESISTANCE in conf:
+            cg.add(var.set_shunt_resistance(i, conf[CONF_SHUNT_RESISTANCE]))
+        if CONF_BUS_VOLTAGE in conf:
+            sens = yield sensor.new_sensor(conf[CONF_BUS_VOLTAGE])
+            cg.add(var.set_bus_voltage_sensor(i, sens))
+        if CONF_SHUNT_VOLTAGE in conf:
+            sens = yield sensor.new_sensor(conf[CONF_SHUNT_VOLTAGE])
+            cg.add(var.set_shunt_voltage_sensor(i, sens))
+        if CONF_CURRENT in conf:
+            sens = yield sensor.new_sensor(conf[CONF_CURRENT])
+            cg.add(var.set_current_sensor(i, sens))
+        if CONF_POWER in conf:
+            sens = yield sensor.new_sensor(conf[CONF_POWER])
+            cg.add(var.set_power_sensor(i, sens))