🏗 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/stepper/stepper.h

@@ -0,0 +1,70 @@
+#pragma once
+
+#include "esphome/core/component.h"
+#include "esphome/core/automation.h"
+#include "esphome/components/stepper/stepper.h"
+
+namespace esphome {
+namespace stepper {
+
+#define LOG_STEPPER(this) \
+  ESP_LOGCONFIG(TAG, "  Acceleration: %.0f steps/s^2", this->acceleration_); \
+  ESP_LOGCONFIG(TAG, "  Deceleration: %.0f steps/s^2", this->deceleration_); \
+  ESP_LOGCONFIG(TAG, "  Max Speed: %.0f steps/s", this->max_speed_);
+
+class Stepper {
+ public:
+  void set_target(int32_t steps) { this->target_position = steps; }
+  void report_position(int32_t steps) { this->current_position = steps; }
+  void set_acceleration(float acceleration) { this->acceleration_ = acceleration; }
+  void set_deceleration(float deceleration) { this->deceleration_ = deceleration; }
+  void set_max_speed(float max_speed) { this->max_speed_ = max_speed; }
+  bool has_reached_target() { return this->current_position == this->target_position; }
+
+  int32_t current_position{0};
+  int32_t target_position{0};
+
+ protected:
+  void calculate_speed_(uint32_t now);
+  int32_t should_step_();
+
+  float acceleration_{1e6f};
+  float deceleration_{1e6f};
+  float current_speed_{0.0f};
+  float max_speed_{1e6f};
+  uint32_t last_calculation_{0};
+  uint32_t last_step_{0};
+};
+
+template<typename... Ts> class SetTargetAction : public Action<Ts...> {
+ public:
+  explicit SetTargetAction(Stepper *parent) : parent_(parent) {}
+
+  TEMPLATABLE_VALUE(int32_t, target)
+
+  void play(Ts... x) override {
+    this->parent_->set_target(this->target_.value(x...));
+    this->play_next(x...);
+  }
+
+ protected:
+  Stepper *parent_;
+};
+
+template<typename... Ts> class ReportPositionAction : public Action<Ts...> {
+ public:
+  explicit ReportPositionAction(Stepper *parent) : parent_(parent) {}
+
+  TEMPLATABLE_VALUE(int32_t, position)
+
+  void play(Ts... x) override {
+    this->parent_->report_position(this->position_.value(x...));
+    this->play_next(x...);
+  }
+
+ protected:
+  Stepper *parent_;
+};
+
+}  // namespace stepper
+}  // namespace esphome