🏗 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/bang_bang/climate.py

@@ -0,0 +1,57 @@
+import esphome.codegen as cg
+import esphome.config_validation as cv
+from esphome import automation
+from esphome.components import climate, sensor
+from esphome.const import CONF_AWAY_CONFIG, CONF_COOL_ACTION, \
+    CONF_DEFAULT_TARGET_TEMPERATURE_HIGH, CONF_DEFAULT_TARGET_TEMPERATURE_LOW, CONF_HEAT_ACTION, \
+    CONF_ID, CONF_IDLE_ACTION, CONF_NAME, CONF_SENSOR
+
+bang_bang_ns = cg.esphome_ns.namespace('bang_bang')
+BangBangClimate = bang_bang_ns.class_('BangBangClimate', climate.ClimateDevice)
+BangBangClimateTargetTempConfig = bang_bang_ns.struct('BangBangClimateTargetTempConfig')
+
+CONFIG_SCHEMA = cv.nameable(climate.CLIMATE_SCHEMA.extend({
+    cv.GenerateID(): cv.declare_variable_id(BangBangClimate),
+    cv.Required(CONF_SENSOR): cv.use_variable_id(sensor.Sensor),
+    cv.Required(CONF_DEFAULT_TARGET_TEMPERATURE_LOW): cv.temperature,
+    cv.Required(CONF_DEFAULT_TARGET_TEMPERATURE_HIGH): cv.temperature,
+    cv.Required(CONF_IDLE_ACTION): automation.validate_automation(single=True),
+    cv.Optional(CONF_COOL_ACTION): automation.validate_automation(single=True),
+    cv.Optional(CONF_HEAT_ACTION): automation.validate_automation(single=True),
+    cv.Optional(CONF_AWAY_CONFIG): cv.Schema({
+        cv.Required(CONF_DEFAULT_TARGET_TEMPERATURE_LOW): cv.temperature,
+        cv.Required(CONF_DEFAULT_TARGET_TEMPERATURE_HIGH): cv.temperature,
+    }),
+}).extend(cv.COMPONENT_SCHEMA), cv.has_at_least_one_key(CONF_COOL_ACTION, CONF_HEAT_ACTION))
+
+
+def to_code(config):
+    var = cg.new_Pvariable(config[CONF_ID], config[CONF_NAME])
+    yield cg.register_component(var, config)
+    yield climate.register_climate(var, config)
+
+    sens = yield cg.get_variable(config[CONF_SENSOR])
+    cg.add(var.set_sensor(sens))
+
+    normal_config = BangBangClimateTargetTempConfig(
+        config[CONF_DEFAULT_TARGET_TEMPERATURE_LOW],
+        config[CONF_DEFAULT_TARGET_TEMPERATURE_HIGH]
+    )
+    cg.add(var.set_normal_config(normal_config))
+
+    yield automation.build_automation(var.get_idle_trigger(), [], config[CONF_IDLE_ACTION])
+
+    if CONF_COOL_ACTION in config:
+        yield automation.build_automation(var.get_cool_trigger(), [], config[CONF_COOL_ACTION])
+        cg.add(var.set_supports_cool(True))
+    if CONF_HEAT_ACTION in config:
+        yield automation.build_automation(var.get_heat_trigger(), [], config[CONF_HEAT_ACTION])
+        cg.add(var.set_supports_heat(True))
+
+    if CONF_AWAY_CONFIG in config:
+        away = config[CONF_AWAY_CONFIG]
+        away_config = BangBangClimateTargetTempConfig(
+            away[CONF_DEFAULT_TARGET_TEMPERATURE_LOW],
+            away[CONF_DEFAULT_TARGET_TEMPERATURE_HIGH]
+        )
+        cg.add(var.set_away_config(away_config))