🏗 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/globals/__init__.py

@@ -0,0 +1,39 @@
+import hashlib
+
+from esphome import config_validation as cv
+from esphome import codegen as cg
+from esphome.const import CONF_ID, CONF_INITIAL_VALUE, CONF_RESTORE_VALUE, CONF_TYPE
+from esphome.py_compat import IS_PY3
+
+globals_ns = cg.esphome_ns.namespace('globals')
+GlobalsComponent = globals_ns.class_('GlobalsComponent', cg.Component)
+
+MULTI_CONF = True
+
+CONFIG_SCHEMA = cv.Schema({
+    cv.Required(CONF_ID): cv.declare_variable_id(GlobalsComponent),
+    cv.Required(CONF_TYPE): cv.string_strict,
+    cv.Optional(CONF_INITIAL_VALUE): cv.string_strict,
+    cv.Optional(CONF_RESTORE_VALUE): cv.boolean,
+}).extend(cv.COMPONENT_SCHEMA)
+
+
+def to_code(config):
+    type_ = cg.RawExpression(config[CONF_TYPE])
+    template_args = cg.TemplateArguments(type_)
+    res_type = GlobalsComponent.template(template_args)
+
+    initial_value = None
+    if CONF_INITIAL_VALUE in config:
+        initial_value = cg.RawExpression(config[CONF_INITIAL_VALUE])
+
+    rhs = GlobalsComponent.new(template_args, initial_value)
+    glob = cg.Pvariable(config[CONF_ID], rhs, type=res_type)
+    yield cg.register_component(glob, config)
+
+    if config.get(CONF_RESTORE_VALUE, False):
+        value = config[CONF_ID].id
+        if IS_PY3 and isinstance(value, str):
+            value = value.encode()
+        hash_ = int(hashlib.md5(value).hexdigest()[:8], 16)
+        cg.add(glob.set_restore_value(hash_))

esphome/components/globals/globals_component.h

@@ -0,0 +1,53 @@
+#pragma once
+
+#include "esphome/core/component.h"
+#include "esphome/core/automation.h"
+
+namespace esphome {
+namespace globals {
+
+template<typename T> class GlobalsComponent : public Component {
+ public:
+  explicit GlobalsComponent() = default;
+  explicit GlobalsComponent(T initial_value) : value_(initial_value) {}
+  explicit GlobalsComponent(std::array<typename std::remove_extent<T>::type, std::extent<T>::value> initial_value) {
+    memcpy(this->value_, initial_value.data(), sizeof(T));
+  }
+
+  T &value() { return this->value_; }
+
+  void setup() override {
+    if (this->restore_value_) {
+      this->rtc_ = global_preferences.make_preference<T>(1944399030U ^ this->name_hash_);
+      this->rtc_.load(&this->value_);
+    }
+    memcpy(&this->prev_value_, &this->value_, sizeof(T));
+  }
+
+  float get_setup_priority() const override { return setup_priority::HARDWARE; }
+
+  void loop() override {
+    if (this->restore_value_) {
+      int diff = memcmp(&this->value_, &this->prev_value_, sizeof(T));
+      if (diff != 0) {
+        this->rtc_.save(&this->value_);
+        memcpy(&this->prev_value_, &this->value_, sizeof(T));
+      }
+    }
+  }
+
+  void set_restore_value(uint32_t name_hash) {
+    this->restore_value_ = true;
+    this->name_hash_ = name_hash;
+  }
+
+ protected:
+  T value_{};
+  T prev_value_{};
+  bool restore_value_{false};
+  uint32_t name_hash_{};
+  ESPPreferenceObject rtc_;
+};
+
+}  // namespace globals
+}  // namespace esphome