🏗 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).

tests/test3.yaml

@@ -2,11 +2,6 @@ esphome:
   name: $devicename
   platform: ESP8266
   board: esp07
-  # Use this for testing while developing:
-  # Note the travis check for esphome PRs will fail until the
-  # esphome-core PR has been merged.
-  # esphome_core_version:
-  #   local: ~/path/to/esphome-core
   build_path: build/test3
 
 substitutions:
@@ -44,39 +39,6 @@ deep_sleep:
   sleep_duration: 50s
 
 sensor:
-  - platform: pmsx003
-    type: PMSX003
-    pm_1_0:
-      name: "PM 1.0 Concentration"
-    pm_2_5:
-      name: "PM 2.5 Concentration"
-    pm_10_0:
-      name: "PM 10.0 Concentration"
-  - platform: pmsx003
-    type: PMS5003T
-    pm_2_5:
-      name: "PM 2.5 Concentration"
-    temperature:
-      name: "PMS Temperature"
-    humidity:
-      name: "PMS Humidity"
-  - platform: pmsx003
-    type: PMS5003ST
-    pm_2_5:
-      name: "PM 2.5 Concentration"
-    temperature:
-      name: "PMS Temperature"
-    humidity:
-      name: "PMS Humidity"
-    formaldehyde:
-      name: "PMS Formaldehyde Concentration"
-  - platform: cse7766
-    voltage:
-      name: "CSE7766 Voltage"
-    current:
-      name: "CSE7766 Current"
-    power:
-      name: "CSE776 Power"
   - platform: apds9960
     type: proximity
     name: APDS9960 Proximity