🏗 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/custom_component/__init__.py

@@ -0,0 +1,26 @@
+import esphome.codegen as cg
+import esphome.config_validation as cv
+from esphome.const import CONF_COMPONENTS, CONF_ID, CONF_LAMBDA
+
+custom_component_ns = cg.esphome_ns.namespace('custom_component')
+CustomComponentConstructor = custom_component_ns.class_('CustomComponentConstructor')
+
+MULTI_CONF = True
+CONFIG_SCHEMA = cv.Schema({
+    cv.GenerateID(): cv.declare_variable_id(CustomComponentConstructor),
+    cv.Required(CONF_LAMBDA): cv.lambda_,
+    cv.Optional(CONF_COMPONENTS): cv.ensure_list(cv.Schema({
+        cv.GenerateID(): cv.declare_variable_id(cg.Component)
+    }).extend(cv.COMPONENT_SCHEMA)),
+})
+
+
+def to_code(config):
+    template_ = yield cg.process_lambda(
+        config[CONF_LAMBDA], [], return_type=cg.std_vector.template(cg.ComponentPtr))
+
+    rhs = CustomComponentConstructor(template_)
+    var = cg.variable(config[CONF_ID], rhs)
+    for i, conf in enumerate(config.get(CONF_COMPONENTS, [])):
+        comp = cg.Pvariable(conf[CONF_ID], var.get_component(i))
+        yield cg.register_component(comp, conf)

esphome/components/custom_component/custom_component.h

@@ -0,0 +1,26 @@
+#pragma once
+
+#include "esphome/core/component.h"
+#include "esphome/core/application.h"
+
+namespace esphome {
+namespace custom_component {
+
+class CustomComponentConstructor {
+ public:
+  CustomComponentConstructor(const std::function<std::vector<Component *>()> &init) {
+    this->components_ = init();
+
+    for (auto *comp : this->components_) {
+      App.register_component(comp);
+    }
+  }
+
+  Component *get_component(int i) { return this->components_[i]; }
+
+ protected:
+  std::vector<Component *> components_;
+};
+
+}  // namespace custom_component
+}  // namespace esphome