🏗 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/uln2003/stepper.py

@@ -0,0 +1,41 @@
+from esphome import pins
+from esphome.components import stepper
+import esphome.config_validation as cv
+import esphome.codegen as cg
+from esphome.const import CONF_ID, CONF_PIN_A, CONF_PIN_B, CONF_PIN_C, CONF_PIN_D, \
+    CONF_SLEEP_WHEN_DONE, CONF_STEP_MODE
+
+
+uln2003_ns = cg.esphome_ns.namespace('uln2003')
+ULN2003StepMode = uln2003_ns.enum('ULN2003StepMode')
+
+STEP_MODES = {
+    'FULL_STEP': ULN2003StepMode.ULN2003_STEP_MODE_FULL_STEP,
+    'HALF_STEP': ULN2003StepMode.ULN2003_STEP_MODE_HALF_STEP,
+    'WAVE_DRIVE': ULN2003StepMode.ULN2003_STEP_MODE_WAVE_DRIVE,
+}
+
+ULN2003 = uln2003_ns.class_('ULN2003', stepper.Stepper, cg.Component)
+
+CONFIG_SCHEMA = stepper.STEPPER_SCHEMA.extend({
+    cv.Required(CONF_ID): cv.declare_variable_id(ULN2003),
+    cv.Required(CONF_PIN_A): pins.gpio_output_pin_schema,
+    cv.Required(CONF_PIN_B): pins.gpio_output_pin_schema,
+    cv.Required(CONF_PIN_C): pins.gpio_output_pin_schema,
+    cv.Required(CONF_PIN_D): pins.gpio_output_pin_schema,
+    cv.Optional(CONF_SLEEP_WHEN_DONE, default=False): cv.boolean,
+    cv.Optional(CONF_STEP_MODE, default='FULL_STEP'): cv.one_of(*STEP_MODES, upper=True, space='_')
+}).extend(cv.COMPONENT_SCHEMA)
+
+
+def to_code(config):
+    pin_a = yield cg.gpio_pin_expression(config[CONF_PIN_A])
+    pin_b = yield cg.gpio_pin_expression(config[CONF_PIN_B])
+    pin_c = yield cg.gpio_pin_expression(config[CONF_PIN_C])
+    pin_d = yield cg.gpio_pin_expression(config[CONF_PIN_D])
+    var = cg.new_Pvariable(config[CONF_ID], pin_a, pin_b, pin_c, pin_d)
+    yield cg.register_component(var, config)
+    yield stepper.register_stepper(var, config)
+
+    cg.add(var.set_sleep_when_done(config[CONF_SLEEP_WHEN_DONE]))
+    cg.add(var.set_step_mode(STEP_MODES[config[CONF_STEP_MODE]]))