🏗 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/ads1115/sensor.py

@@ -0,0 +1,64 @@
+import esphome.codegen as cg
+import esphome.config_validation as cv
+from esphome.components import sensor
+from esphome.components.ads1115 import ADS1115Component
+from esphome.const import CONF_GAIN, CONF_MULTIPLEXER, CONF_UPDATE_INTERVAL, \
+    ICON_FLASH, UNIT_VOLT, CONF_ID, CONF_NAME
+from esphome.py_compat import string_types
+from . import ads1115_ns
+
+DEPENDENCIES = ['ads1115']
+
+ADS1115Multiplexer = ads1115_ns.enum('ADS1115Multiplexer')
+MUX = {
+    'A0_A1': ADS1115Multiplexer.ADS1115_MULTIPLEXER_P0_N1,
+    'A0_A3': ADS1115Multiplexer.ADS1115_MULTIPLEXER_P0_N3,
+    'A1_A3': ADS1115Multiplexer.ADS1115_MULTIPLEXER_P1_N3,
+    'A2_A3': ADS1115Multiplexer.ADS1115_MULTIPLEXER_P2_N3,
+    'A0_GND': ADS1115Multiplexer.ADS1115_MULTIPLEXER_P0_NG,
+    'A1_GND': ADS1115Multiplexer.ADS1115_MULTIPLEXER_P1_NG,
+    'A2_GND': ADS1115Multiplexer.ADS1115_MULTIPLEXER_P2_NG,
+    'A3_GND': ADS1115Multiplexer.ADS1115_MULTIPLEXER_P3_NG,
+}
+
+ADS1115Gain = ads1115_ns.enum('ADS1115Gain')
+GAIN = {
+    '6.144': ADS1115Gain.ADS1115_GAIN_6P144,
+    '4.096': ADS1115Gain.ADS1115_GAIN_4P096,
+    '2.048': ADS1115Gain.ADS1115_GAIN_2P048,
+    '1.024': ADS1115Gain.ADS1115_GAIN_1P024,
+    '0.512': ADS1115Gain.ADS1115_GAIN_0P512,
+    '0.256': ADS1115Gain.ADS1115_GAIN_0P256,
+}
+
+
+def validate_gain(value):
+    if isinstance(value, float):
+        value = u'{:0.03f}'.format(value)
+    elif not isinstance(value, string_types):
+        raise cv.Invalid('invalid gain "{}"'.format(value))
+
+    return cv.one_of(*GAIN)(value)
+
+
+ADS1115Sensor = ads1115_ns.class_('ADS1115Sensor', sensor.Sensor)
+
+
+CONF_ADS1115_ID = 'ads1115_id'
+CONFIG_SCHEMA = cv.nameable(sensor.sensor_schema(UNIT_VOLT, ICON_FLASH, 3).extend({
+    cv.GenerateID(): cv.declare_variable_id(ADS1115Sensor),
+    cv.GenerateID(CONF_ADS1115_ID): cv.use_variable_id(ADS1115Component),
+    cv.Required(CONF_MULTIPLEXER): cv.one_of(*MUX, upper=True, space='_'),
+    cv.Required(CONF_GAIN): validate_gain,
+    cv.Optional(CONF_UPDATE_INTERVAL, default='60s'): cv.update_interval,
+}))
+
+
+def to_code(config):
+    hub = yield cg.get_variable(config[CONF_ADS1115_ID])
+    var = cg.new_Pvariable(config[CONF_ID], config[CONF_NAME], config[CONF_UPDATE_INTERVAL])
+    cg.add(var.set_multiplexer(MUX[config[CONF_MULTIPLEXER]]))
+    cg.add(var.set_gain(GAIN[config[CONF_GAIN]]))
+    yield sensor.register_sensor(var, config)
+
+    cg.add(hub.register_sensor(var))