🏗 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/dallas/dallas_component.h

@@ -0,0 +1,78 @@
+#pragma once
+
+#include "esphome/core/component.h"
+#include "esphome/components/sensor/sensor.h"
+#include "esp_one_wire.h"
+
+namespace esphome {
+namespace dallas {
+
+class DallasTemperatureSensor;
+
+class DallasComponent : public PollingComponent {
+ public:
+  explicit DallasComponent(ESPOneWire *one_wire, uint32_t update_interval);
+
+  DallasTemperatureSensor *get_sensor_by_address(const std::string &name, uint64_t address, uint8_t resolution);
+  DallasTemperatureSensor *get_sensor_by_index(const std::string &name, uint8_t index, uint8_t resolution);
+
+  void setup() override;
+  void dump_config() override;
+  float get_setup_priority() const override { return setup_priority::DATA; }
+
+  void update() override;
+
+ protected:
+  friend DallasTemperatureSensor;
+
+  ESPOneWire *one_wire_;
+  std::vector<DallasTemperatureSensor *> sensors_;
+  std::vector<uint64_t> found_sensors_;
+};
+
+/// Internal class that helps us create multiple sensors for one Dallas hub.
+class DallasTemperatureSensor : public sensor::Sensor {
+ public:
+  DallasTemperatureSensor(const std::string &name, uint64_t address, uint8_t resolution, DallasComponent *parent);
+
+  /// Helper to get a pointer to the address as uint8_t.
+  uint8_t *get_address8();
+  /// Helper to create (and cache) the name for this sensor. For example "0xfe0000031f1eaf29".
+  const std::string &get_address_name();
+
+  /// Set the 64-bit unsigned address for this sensor.
+  void set_address(uint64_t address);
+  /// Get the index of this sensor. (0 if using address.)
+  optional<uint8_t> get_index() const;
+  /// Set the index of this sensor. If using index, address will be set after setup.
+  void set_index(uint8_t index);
+  /// Get the set resolution for this sensor.
+  uint8_t get_resolution() const;
+  /// Set the resolution for this sensor.
+  void set_resolution(uint8_t resolution);
+  /// Get the number of milliseconds we have to wait for the conversion phase.
+  uint16_t millis_to_wait_for_conversion() const;
+
+  bool setup_sensor();
+  bool read_scratch_pad();
+
+  bool check_scratch_pad();
+
+  float get_temp_c();
+
+  std::string unique_id() override;
+
+ protected:
+  DallasComponent *parent_;
+  uint64_t address_;
+  optional<uint8_t> index_;
+
+  uint8_t resolution_;
+  std::string address_name_;
+  uint8_t scratch_pad_[9] = {
+      0,
+  };
+};
+
+}  // namespace dallas
+}  // namespace esphome