🏗 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).

requirements_test.txt

@@ -0,0 +1,18 @@
+voluptuous>=0.11.5,<0.12
+PyYAML>=5.1,<6
+paho-mqtt>=1.4,<2
+colorlog>=4.0.2
+tornado>=5.1.1,<6
+typing>=3.6.6 ; python_version<"3.5"
+protobuf>=3.7,<3.8
+tzlocal>=1.5.1
+pyserial>=3.4,<4
+ifaddr>=0.1.6,<1
+platformio>=3.6.5 ; python_version<"3"
+https://github.com/platformio/platformio-core/archive/develop.zip ; python_version>"3"
+esptool>=2.6,<3
+pylint==1.9.4 ; python_version<"3"
+pylint==2.3.0 ; python_version>"3"
+flake8==3.6.0
+pillow
+pexpect