🏗 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/hlw8012/sensor.py

@@ -0,0 +1,57 @@
+import esphome.codegen as cg
+import esphome.config_validation as cv
+from esphome import pins
+from esphome.components import sensor
+from esphome.const import CONF_CHANGE_MODE_EVERY, CONF_CURRENT, \
+    CONF_CURRENT_RESISTOR, CONF_ID, CONF_POWER, CONF_SEL_PIN, CONF_UPDATE_INTERVAL, \
+    CONF_VOLTAGE, CONF_VOLTAGE_DIVIDER, ICON_FLASH, UNIT_VOLT, UNIT_AMPERE, UNIT_WATT
+
+AUTO_LOAD = ['pulse_width']
+
+hlw8012_ns = cg.esphome_ns.namespace('hlw8012')
+HLW8012Component = hlw8012_ns.class_('HLW8012Component', cg.PollingComponent)
+
+CONF_CF1_PIN = 'cf1_pin'
+CONF_CF_PIN = 'cf_pin'
+CONFIG_SCHEMA = cv.Schema({
+    cv.GenerateID(): cv.declare_variable_id(HLW8012Component),
+    cv.Required(CONF_SEL_PIN): pins.gpio_output_pin_schema,
+    cv.Required(CONF_CF_PIN): cv.All(pins.internal_gpio_input_pullup_pin_schema,
+                                     pins.validate_has_interrupt),
+    cv.Required(CONF_CF1_PIN): cv.All(pins.internal_gpio_input_pullup_pin_schema,
+                                      pins.validate_has_interrupt),
+
+    cv.Optional(CONF_VOLTAGE): cv.nameable(sensor.sensor_schema(UNIT_VOLT, ICON_FLASH, 1)),
+    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, 1)),
+
+    cv.Optional(CONF_CURRENT_RESISTOR, default=0.001): cv.resistance,
+    cv.Optional(CONF_VOLTAGE_DIVIDER, default=2351): cv.positive_float,
+    cv.Optional(CONF_CHANGE_MODE_EVERY, default=8): cv.All(cv.uint32_t, cv.Range(min=1)),
+    cv.Optional(CONF_UPDATE_INTERVAL, default='60s'): cv.update_interval,
+}).extend(cv.COMPONENT_SCHEMA)
+
+
+def to_code(config):
+    var = cg.new_Pvariable(config[CONF_ID], config[CONF_UPDATE_INTERVAL])
+    yield cg.register_component(var, config)
+
+    sel = yield cg.gpio_pin_expression(config[CONF_SEL_PIN])
+    cg.add(var.set_sel_pin(sel))
+    cf = yield cg.gpio_pin_expression(config[CONF_CF_PIN])
+    cg.add(var.set_cf_pin(cf))
+    cf1 = yield cg.gpio_pin_expression(config[CONF_CF1_PIN])
+    cg.add(var.set_cf1_pin(cf1))
+
+    if CONF_VOLTAGE in config:
+        sens = yield sensor.new_sensor(config[CONF_VOLTAGE])
+        cg.add(var.set_voltage_sensor(sens))
+    if CONF_CURRENT in config:
+        sens = yield sensor.new_sensor(config[CONF_CURRENT])
+        cg.add(var.set_current_sensor(sens))
+    if CONF_POWER in config:
+        sens = yield sensor.new_sensor(config[CONF_POWER])
+        cg.add(var.set_power_sensor(sens))
+    cg.add(var.set_current_resistor(config[CONF_CURRENT_RESISTOR]))
+    cg.add(var.set_voltage_divider(config[CONF_VOLTAGE_DIVIDER]))
+    cg.add(var.set_change_mode_every(config[CONF_CHANGE_MODE_EVERY]))