🏗 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/cse7766/cse7766.h

@@ -0,0 +1,43 @@
+#pragma once
+
+#include "esphome/core/component.h"
+#include "esphome/components/sensor/sensor.h"
+#include "esphome/components/uart/uart.h"
+
+namespace esphome {
+namespace cse7766 {
+
+class CSE7766Component : public PollingComponent, public uart::UARTDevice {
+ public:
+  CSE7766Component(uint32_t update_interval) : PollingComponent(update_interval) {}
+
+  void set_voltage_sensor(sensor::Sensor *voltage_sensor) { voltage_sensor_ = voltage_sensor; }
+  void set_current_sensor(sensor::Sensor *current_sensor) { current_sensor_ = current_sensor; }
+  void set_power_sensor(sensor::Sensor *power_sensor) { power_sensor_ = power_sensor; }
+
+  void loop() override;
+  float get_setup_priority() const override;
+  void update() override;
+  void dump_config() override;
+
+ protected:
+  bool check_byte_();
+  void parse_data_();
+  uint32_t get_24_bit_uint_(uint8_t start_index);
+
+  uint8_t raw_data_[24];
+  uint8_t raw_data_index_{0};
+  uint32_t last_transmission_{0};
+  sensor::Sensor *voltage_sensor_{nullptr};
+  sensor::Sensor *current_sensor_{nullptr};
+  sensor::Sensor *power_sensor_{nullptr};
+  float voltage_acc_{0.0f};
+  float current_acc_{0.0f};
+  float power_acc_{0.0f};
+  uint32_t voltage_counts_{0};
+  uint32_t current_counts_{0};
+  uint32_t power_counts_{0};
+};
+
+}  // namespace cse7766
+}  // namespace esphome