🏗 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/uart/uart.h

@@ -0,0 +1,121 @@
+#pragma once
+
+#include <HardwareSerial.h>
+#include "esphome/core/esphal.h"
+#include "esphome/core/component.h"
+
+namespace esphome {
+namespace uart {
+
+#ifdef ARDUINO_ARCH_ESP8266
+class ESP8266SoftwareSerial {
+ public:
+  void setup(int8_t tx_pin, int8_t rx_pin, uint32_t baud_rate);
+
+  uint8_t read_byte();
+  uint8_t peek_byte();
+
+  void flush();
+
+  void write_byte(uint8_t data);
+
+  int available();
+
+ protected:
+  static void gpio_intr(ESP8266SoftwareSerial *arg);
+
+  inline void wait_(uint32_t *wait, const uint32_t &start);
+  inline bool read_bit_(uint32_t *wait, const uint32_t &start);
+  inline void write_bit_(bool bit, uint32_t *wait, const uint32_t &start);
+
+  uint32_t bit_time_{0};
+  uint8_t *rx_buffer_{nullptr};
+  size_t rx_buffer_size_{64};
+  volatile size_t rx_in_pos_{0};
+  size_t rx_out_pos_{0};
+  ISRInternalGPIOPin *tx_pin_{nullptr};
+  ISRInternalGPIOPin *rx_pin_{nullptr};
+};
+#endif
+
+class UARTComponent : public Component, public Stream {
+ public:
+  UARTComponent(uint32_t baud_rate) : baud_rate_(baud_rate) {}
+
+  void setup() override;
+
+  void dump_config() override;
+
+  void write_byte(uint8_t data);
+
+  void write_array(const uint8_t *data, size_t len);
+
+  void write_str(const char *str);
+
+  bool peek_byte(uint8_t *data);
+
+  bool read_byte(uint8_t *data);
+
+  bool read_array(uint8_t *data, size_t len);
+
+  int available() override;
+
+  void flush() override;
+
+  float get_setup_priority() const override { return setup_priority::BUS; }
+
+  size_t write(uint8_t data) override;
+  int read() override;
+  int peek() override;
+
+  void set_tx_pin(uint8_t tx_pin) { this->tx_pin_ = tx_pin; }
+  void set_rx_pin(uint8_t rx_pin) { this->rx_pin_ = rx_pin; }
+
+ protected:
+  bool check_read_timeout_(size_t len = 1);
+
+  HardwareSerial *hw_serial_{nullptr};
+#ifdef ARDUINO_ARCH_ESP8266
+  ESP8266SoftwareSerial *sw_serial_{nullptr};
+#endif
+  optional<uint8_t> tx_pin_;
+  optional<uint8_t> rx_pin_;
+  uint32_t baud_rate_;
+};
+
+#ifdef ARDUINO_ARCH_ESP32
+extern uint8_t next_uart_num;
+#endif
+
+class UARTDevice : public Stream {
+ public:
+  UARTDevice() = default;
+  UARTDevice(UARTComponent *parent) : parent_(parent) {}
+
+  void set_uart_parent(UARTComponent *parent) { this->parent_ = parent; }
+
+  void write_byte(uint8_t data) { this->parent_->write_byte(data); }
+
+  void write_array(const uint8_t *data, size_t len) { this->parent_->write_array(data, len); }
+
+  void write_str(const char *str) { this->parent_->write_str(str); }
+
+  bool read_byte(uint8_t *data) { return this->parent_->read_byte(data); }
+  bool peek_byte(uint8_t *data) { return this->parent_->peek_byte(data); }
+
+  bool read_array(uint8_t *data, size_t len) { return this->parent_->read_array(data, len); }
+
+  int available() override { return this->parent_->available(); }
+
+  void flush() override { return this->parent_->flush(); }
+
+  size_t write(uint8_t data) override { return this->parent_->write(data); }
+  int read() override { return this->parent_->read(); }
+  int peek() override { return this->parent_->peek(); }
+
+ protected:
+  UARTComponent *parent_{nullptr};
+};
+
+}  // namespace uart
+}  // namespace esphome