🏗 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/binary_sensor/binary_sensor.h

@@ -0,0 +1,90 @@
+#pragma once
+
+#include "esphome/core/component.h"
+#include "esphome/core/helpers.h"
+#include "esphome/components/binary_sensor/filter.h"
+
+namespace esphome {
+
+namespace binary_sensor {
+
+#define LOG_BINARY_SENSOR(prefix, type, obj) \
+  if (obj != nullptr) { \
+    ESP_LOGCONFIG(TAG, prefix type " '%s'", obj->get_name().c_str()); \
+    if (!obj->get_device_class().empty()) { \
+      ESP_LOGCONFIG(TAG, prefix "  Device Class: '%s'", obj->get_device_class().c_str()); \
+    } \
+  }
+
+/** Base class for all binary_sensor-type classes.
+ *
+ * This class includes a callback that components such as MQTT can subscribe to for state changes.
+ * The sub classes should notify the front-end of new states via the publish_state() method which
+ * handles inverted inputs for you.
+ */
+class BinarySensor : public Nameable {
+ public:
+  /** Construct a binary sensor with the specified name
+   *
+   * @param name Name of this binary sensor.
+   */
+  explicit BinarySensor(const std::string &name);
+  explicit BinarySensor();
+
+  /** Add a callback to be notified of state changes.
+   *
+   * @param callback The void(bool) callback.
+   */
+  void add_on_state_callback(std::function<void(bool)> &&callback);
+
+  /** Publish a new state to the front-end.
+   *
+   * @param state The new state.
+   */
+  void publish_state(bool state);
+
+  /** Publish the initial state, this will not make the callback manager send callbacks
+   * and is meant only for the initial state on boot.
+   *
+   * @param state The new state.
+   */
+  void publish_initial_state(bool state);
+
+  /// The current reported state of the binary sensor.
+  bool state;
+
+  /// Manually set the Home Assistant device class (see binary_sensor::device_class)
+  void set_device_class(const std::string &device_class);
+
+  /// Get the device class for this binary sensor, using the manual override if specified.
+  std::string get_device_class();
+
+  void add_filter(Filter *filter);
+  void add_filters(std::vector<Filter *> filters);
+
+  // ========== INTERNAL METHODS ==========
+  // (In most use cases you won't need these)
+  void send_state_internal(bool state, bool is_initial);
+
+  /// Return whether this binary sensor has outputted a state.
+  bool has_state() const;
+
+  virtual bool is_status_binary_sensor() const;
+
+  // ========== OVERRIDE METHODS ==========
+  // (You'll only need this when creating your own custom binary sensor)
+  /// Get the default device class for this sensor, or empty string for no default.
+  virtual std::string device_class();
+
+ protected:
+  uint32_t hash_base() override;
+
+  CallbackManager<void(bool)> state_callback_{};
+  optional<std::string> device_class_{};  ///< Stores the override of the device class
+  Filter *filter_list_{nullptr};
+  bool has_state_{false};
+  Deduplicator<bool> publish_dedup_;
+};
+
+}  // namespace binary_sensor
+}  // namespace esphome