🏗 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/i2c/__init__.py

@@ -0,0 +1,47 @@
+import esphome.codegen as cg
+import esphome.config_validation as cv
+from esphome import pins
+from esphome.const import CONF_FREQUENCY, CONF_ID, CONF_SCAN, CONF_SCL, CONF_SDA, CONF_ADDRESS, \
+    CONF_I2C_ID
+from esphome.core import coroutine
+
+i2c_ns = cg.esphome_ns.namespace('i2c')
+I2CComponent = i2c_ns.class_('I2CComponent', cg.Component)
+I2CDevice = i2c_ns.class_('I2CDevice')
+
+MULTI_CONF = True
+CONFIG_SCHEMA = cv.Schema({
+    cv.GenerateID(): cv.declare_variable_id(I2CComponent),
+    cv.Optional(CONF_SDA, default='SDA'): pins.input_pin,
+    cv.Optional(CONF_SCL, default='SCL'): pins.input_pin,
+    cv.Optional(CONF_FREQUENCY, default='50kHz'):
+        cv.All(cv.frequency, cv.Range(min=0, min_included=False)),
+    cv.Optional(CONF_SCAN, default=True): cv.boolean,
+}).extend(cv.COMPONENT_SCHEMA)
+
+
+def to_code(config):
+    var = cg.new_Pvariable(config[CONF_ID], config[CONF_SDA], config[CONF_SCL],
+                           int(config[CONF_FREQUENCY]), config[CONF_SCAN])
+    yield cg.register_component(var, config)
+
+    cg.add_library('Wire', None)
+    cg.add_global(i2c_ns.using)
+
+
+def i2c_device_schema(default_address):
+    schema = {
+        cv.GenerateID(CONF_I2C_ID): cv.use_variable_id(I2CComponent),
+    }
+    if default_address is None:
+        schema[cv.Required(CONF_ADDRESS)] = cv.i2c_address
+    else:
+        schema[cv.Optional(CONF_ADDRESS, default=default_address)] = cv.i2c_address
+    return cv.Schema(schema)
+
+
+@coroutine
+def register_i2c_device(var, config):
+    parent = yield cg.get_variable(config[CONF_I2C_ID])
+    cg.add(var.set_i2c_parent(parent))
+    cg.add(var.set_i2c_address(config[CONF_ADDRESS]))