🏗 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/cpp_helpers.py

@@ -1,61 +1,43 @@
-from esphome.const import CONF_INVERTED, CONF_MODE, CONF_NUMBER, CONF_PCF8574, \
-    CONF_SETUP_PRIORITY, CONF_MCP23017
-from esphome.core import CORE, EsphomeError, coroutine
-from esphome.cpp_generator import IntLiteral, RawExpression
-from esphome.cpp_types import GPIOInputPin, GPIOOutputPin
+from esphome.const import CONF_INVERTED, CONF_MODE, CONF_NUMBER, CONF_SETUP_PRIORITY
+from esphome.core import coroutine
+from esphome.cpp_generator import RawExpression, add
+from esphome.cpp_types import App, GPIOPin
 
 
 @coroutine
-def generic_gpio_pin_expression_(conf, mock_obj, default_mode):
+def gpio_pin_expression(conf):
     if conf is None:
         return
+    from esphome import pins
+    for key, (_, func) in pins.PIN_SCHEMA_REGISTRY.items():
+        if key in conf:
+            yield coroutine(func)(conf)
+            return
+
     number = conf[CONF_NUMBER]
+    mode = conf[CONF_MODE]
     inverted = conf.get(CONF_INVERTED)
-    if CONF_PCF8574 in conf:
-        from esphome.components import pcf8574
-
-        hub = yield CORE.get_variable(conf[CONF_PCF8574])
-
-        if default_mode == u'INPUT':
-            mode = pcf8574.PCF8675_GPIO_MODES[conf.get(CONF_MODE, u'INPUT')]
-            yield hub.make_input_pin(number, mode, inverted)
-            return
-        if default_mode == u'OUTPUT':
-            yield hub.make_output_pin(number, inverted)
-            return
-
-        raise EsphomeError(u"Unknown default mode {}".format(default_mode))
-    if CONF_MCP23017 in conf:
-        from esphome.components import mcp23017
-
-        hub = yield CORE.get_variable(conf[CONF_MCP23017])
-
-        if default_mode == u'INPUT':
-            mode = mcp23017.MCP23017_GPIO_MODES[conf.get(CONF_MODE, u'INPUT')]
-            yield hub.make_input_pin(number, mode, inverted)
-            return
-        if default_mode == u'OUTPUT':
-            yield hub.make_output_pin(number, inverted)
-            return
-
-        raise EsphomeError(u"Unknown default mode {}".format(default_mode))
-    if len(conf) == 1:
-        yield IntLiteral(number)
-        return
-    mode = RawExpression(conf.get(CONF_MODE, default_mode))
-    yield mock_obj(number, mode, inverted)
+    yield GPIOPin.new(number, RawExpression(mode), inverted)
 
 
 @coroutine
-def gpio_output_pin_expression(conf):
-    yield generic_gpio_pin_expression_(conf, GPIOOutputPin, 'OUTPUT')
-
-
-@coroutine
-def gpio_input_pin_expression(conf):
-    yield generic_gpio_pin_expression_(conf, GPIOInputPin, 'INPUT')
-
-
-def setup_component(obj, config):
+def register_component(obj, config):
     if CONF_SETUP_PRIORITY in config:
-        CORE.add(obj.set_setup_priority(config[CONF_SETUP_PRIORITY]))
+        add(obj.set_setup_priority(config[CONF_SETUP_PRIORITY]))
+    add(App.register_component(obj))
+
+
+@coroutine
+def build_registry_entry(registry, full_config):
+    key, config = next((k, v) for k, v in full_config.items() if k in registry)
+    builder = coroutine(registry[key][1])
+    yield builder(config)
+
+
+@coroutine
+def build_registry_list(registry, config):
+    actions = []
+    for conf in config:
+        action = yield build_registry_entry(registry, conf)
+        actions.append(action)
+    yield actions