🏗 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/ethernet/ethernet_component.h

@@ -0,0 +1,81 @@
+#pragma once
+
+#include "esphome/core/component.h"
+#include "esphome/core/esphal.h"
+
+#ifdef ARDUINO_ARCH_ESP32
+
+#include "esp_eth.h"
+#include <esp_wifi.h>
+#include <WiFiType.h>
+#include <WiFi.h>
+
+namespace esphome {
+namespace ethernet {
+
+enum EthernetType {
+  ETHERNET_TYPE_LAN8720 = 0,
+  ETHERNET_TYPE_TLK110,
+};
+
+struct ManualIP {
+  IPAddress static_ip;
+  IPAddress gateway;
+  IPAddress subnet;
+  IPAddress dns1;  ///< The first DNS server. 0.0.0.0 for default.
+  IPAddress dns2;  ///< The second DNS server. 0.0.0.0 for default.
+};
+
+class EthernetComponent : public Component {
+ public:
+  EthernetComponent();
+  void setup() override;
+  void loop() override;
+  void dump_config() override;
+  float get_setup_priority() const override;
+  bool can_proceed() override;
+  bool is_connected();
+
+  void set_phy_addr(uint8_t phy_addr);
+  void set_power_pin(GPIOPin *power_pin);
+  void set_mdc_pin(uint8_t mdc_pin);
+  void set_mdio_pin(uint8_t mdio_pin);
+  void set_type(EthernetType type);
+  void set_clk_mode(eth_clock_mode_t clk_mode);
+  void set_manual_ip(ManualIP manual_ip);
+
+  IPAddress get_ip_address();
+  std::string get_use_address() const;
+  void set_use_address(const std::string &use_address);
+
+ protected:
+  void on_wifi_event_(system_event_id_t event, system_event_info_t info);
+  void start_connect_();
+  void dump_connect_params_();
+
+  static void eth_phy_config_gpio_();
+  static void eth_phy_power_enable_(bool enable);
+
+  std::string use_address_;
+  uint8_t phy_addr_{0};
+  GPIOPin *power_pin_{nullptr};
+  uint8_t mdc_pin_{23};
+  uint8_t mdio_pin_{18};
+  EthernetType type_{ETHERNET_TYPE_LAN8720};
+  eth_clock_mode_t clk_mode_{ETH_CLOCK_GPIO0_IN};
+  optional<ManualIP> manual_ip_{};
+
+  bool initialized_{false};
+  bool connected_{false};
+  bool last_connected_{false};
+  uint32_t connect_begin_;
+  eth_config_t eth_config;
+  eth_phy_power_enable_func orig_power_enable_fun_;
+};
+
+extern EthernetComponent *global_eth_component;
+
+}  // namespace ethernet
+}  // namespace esphome
+
+#endif