🏗 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/logger/logger.h

@@ -0,0 +1,85 @@
+#pragma once
+
+#include "esphome/core/component.h"
+#include "esphome/core/log.h"
+#include "esphome/core/helpers.h"
+#include "esphome/core/defines.h"
+
+namespace esphome {
+
+namespace logger {
+
+/** Enum for logging UART selection
+ *
+ * Advanced configuration (pin selection, etc) is not supported.
+ */
+enum UARTSelection {
+  UART_SELECTION_UART0 = 0,
+  UART_SELECTION_UART1,
+#ifdef ARDUINO_ARCH_ESP32
+  UART_SELECTION_UART2
+#endif
+#ifdef ARDUINO_ARCH_ESP8266
+      UART_SELECTION_UART0_SWAP
+#endif
+};
+
+class Logger : public Component {
+ public:
+  explicit Logger(uint32_t baud_rate, size_t tx_buffer_size, UARTSelection uart);
+
+  /// Manually set the baud rate for serial, set to 0 to disable.
+  void set_baud_rate(uint32_t baud_rate);
+
+  /// Set the buffer size that's used for constructing log messages. Log messages longer than this will be truncated.
+  void set_tx_buffer_size(size_t tx_buffer_size);
+
+  /// Get the UART used by the logger.
+  UARTSelection get_uart() const;
+
+  /// Set the global log level. Note: Use the ESPHOME_LOG_LEVEL define to also remove the logs from the build.
+  void set_global_log_level(int log_level);
+  int get_global_log_level() const { return this->global_log_level_; }
+
+  /// Set the log level of the specified tag.
+  void set_log_level(const std::string &tag, int log_level);
+
+  // ========== INTERNAL METHODS ==========
+  // (In most use cases you won't need these)
+  /// Set up this component.
+  void pre_setup();
+  void dump_config() override;
+
+  int level_for(const char *tag);
+
+  /// Register a callback that will be called for every log message sent
+  void add_on_log_callback(std::function<void(int, const char *, const char *)> &&callback);
+
+  float get_setup_priority() const override;
+
+  int log_vprintf_(int level, const char *tag, const char *format, va_list args);  // NOLINT
+#ifdef USE_STORE_LOG_STR_IN_FLASH
+  int log_vprintf_(int level, const char *tag, const __FlashStringHelper *format, va_list args);  // NOLINT
+#endif
+
+ protected:
+  void log_message_(int level, const char *tag, char *msg, int ret);
+
+  uint32_t baud_rate_;
+  std::vector<char> tx_buffer_;
+  int global_log_level_{ESPHOME_LOG_LEVEL};
+  UARTSelection uart_{UART_SELECTION_UART0};
+  HardwareSerial *hw_serial_{nullptr};
+  struct LogLevelOverride {
+    std::string tag;
+    int level;
+  };
+  std::vector<LogLevelOverride> log_levels_;
+  CallbackManager<void(int, const char *, const char *)> log_callback_{};
+};
+
+extern Logger *global_logger;
+
+}  // namespace logger
+
+}  // namespace esphome