🏗 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/template/sensor/__init__.py

@@ -0,0 +1,45 @@
+
+from esphome.automation import ACTION_REGISTRY
+from esphome.components import sensor
+import esphome.config_validation as cv
+import esphome.codegen as cg
+from esphome.const import CONF_ID, CONF_LAMBDA, CONF_NAME, CONF_STATE, CONF_UPDATE_INTERVAL
+from .. import template_ns
+
+TemplateSensor = template_ns.class_('TemplateSensor', sensor.PollingSensorComponent)
+
+CONFIG_SCHEMA = cv.nameable(sensor.SENSOR_SCHEMA.extend({
+    cv.GenerateID(): cv.declare_variable_id(TemplateSensor),
+    cv.Optional(CONF_LAMBDA): cv.lambda_,
+    cv.Optional(CONF_UPDATE_INTERVAL, default="60s"): cv.update_interval,
+}).extend(cv.COMPONENT_SCHEMA))
+
+
+def to_code(config):
+    rhs = TemplateSensor.new(config[CONF_NAME], config[CONF_UPDATE_INTERVAL])
+    template = cg.Pvariable(config[CONF_ID], rhs)
+    yield cg.register_component(template, config)
+    yield sensor.register_sensor(template, config)
+
+    if CONF_LAMBDA in config:
+        template_ = yield cg.process_lambda(config[CONF_LAMBDA], [],
+                                            return_type=cg.optional.template(float))
+        cg.add(template.set_template(template_))
+
+
+CONF_SENSOR_TEMPLATE_PUBLISH = 'sensor.template.publish'
+SENSOR_TEMPLATE_PUBLISH_ACTION_SCHEMA = cv.Schema({
+    cv.Required(CONF_ID): cv.use_variable_id(sensor.Sensor),
+    cv.Required(CONF_STATE): cv.templatable(cv.float_),
+})
+
+
+@ACTION_REGISTRY.register(CONF_SENSOR_TEMPLATE_PUBLISH, SENSOR_TEMPLATE_PUBLISH_ACTION_SCHEMA)
+def sensor_template_publish_to_code(config, action_id, template_arg, args):
+    var = yield cg.get_variable(config[CONF_ID])
+    type = sensor.SensorPublishAction.template(template_arg)
+    rhs = type.new(var)
+    action = cg.Pvariable(action_id, rhs, type=type)
+    template_ = yield cg.templatable(config[CONF_STATE], args, float)
+    cg.add(action.set_state(template_))
+    yield action