🏗 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/lcd_pcf8574/display.py

@@ -0,0 +1,20 @@
+import esphome.codegen as cg
+import esphome.config_validation as cv
+from esphome.components import lcd_base, i2c
+from esphome.const import CONF_ID, CONF_UPDATE_INTERVAL
+
+DEPENDENCIES = ['i2c']
+AUTO_LOAD = ['lcd_base']
+
+lcd_pcf8574_ns = cg.esphome_ns.namespace('lcd_pcf8574')
+PCF8574LCDDisplay = lcd_pcf8574_ns.class_('PCF8574LCDDisplay', lcd_base.LCDDisplay, i2c.I2CDevice)
+
+CONFIG_SCHEMA = lcd_base.LCD_SCHEMA.extend({
+    cv.GenerateID(): cv.declare_variable_id(PCF8574LCDDisplay),
+}).extend(i2c.i2c_device_schema(0x3F))
+
+
+def to_code(config):
+    var = cg.new_Pvariable(config[CONF_ID], config[CONF_UPDATE_INTERVAL])
+    yield lcd_base.setup_lcd_display(var, config)
+    yield i2c.register_i2c_device(var, config)

esphome/components/lcd_pcf8574/pcf8574_display.cpp

@@ -0,0 +1,46 @@
+#include "pcf8574_display.h"
+#include "esphome/core/log.h"
+
+namespace esphome {
+namespace lcd_pcf8574 {
+
+static const char *TAG = "lcd_pcf8574";
+
+void PCF8574LCDDisplay::setup() {
+  ESP_LOGCONFIG(TAG, "Setting up PCF8574 LCD Display...");
+  if (!this->write_bytes(0x08, nullptr, 0)) {
+    this->mark_failed();
+    return;
+  }
+
+  LCDDisplay::setup();
+}
+void PCF8574LCDDisplay::dump_config() {
+  ESP_LOGCONFIG(TAG, "PCF8574 LCD Display:");
+  ESP_LOGCONFIG(TAG, "  Columns: %u, Rows: %u", this->columns_, this->rows_);
+  LOG_I2C_DEVICE(this);
+  LOG_UPDATE_INTERVAL(this);
+  if (this->is_failed()) {
+    ESP_LOGE(TAG, "Communication with LCD Display failed!");
+  }
+}
+void PCF8574LCDDisplay::write_n_bits(uint8_t value, uint8_t n) {
+  if (n == 4) {
+    // Ugly fix: in the super setup() with n == 4 value needs to be shifted left
+    value <<= 4;
+  }
+  uint8_t data = value | 0x08;  // Enable backlight
+  this->write_bytes(data, nullptr, 0);
+  // Pulse ENABLE
+  this->write_bytes(data | 0x04, nullptr, 0);
+  delayMicroseconds(1);  // >450ns
+  this->write_bytes(data, nullptr, 0);
+  delayMicroseconds(100);  // >37us
+}
+void PCF8574LCDDisplay::send(uint8_t value, bool rs) {
+  this->write_n_bits((value & 0xF0) | rs, 0);
+  this->write_n_bits(((value << 4) & 0xF0) | rs, 0);
+}
+
+}  // namespace lcd_pcf8574
+}  // namespace esphome

esphome/components/lcd_pcf8574/pcf8574_display.h

@@ -0,0 +1,23 @@
+#pragma once
+
+#include "esphome/core/component.h"
+#include "esphome/components/lcd_base/lcd_display.h"
+#include "esphome/components/i2c/i2c.h"
+
+namespace esphome {
+namespace lcd_pcf8574 {
+
+class PCF8574LCDDisplay : public lcd_base::LCDDisplay, public i2c::I2CDevice {
+ public:
+  PCF8574LCDDisplay(uint32_t update_interval) : lcd_base::LCDDisplay(update_interval) {}
+  void setup() override;
+  void dump_config() override;
+
+ protected:
+  bool is_four_bit_mode() override { return true; }
+  void write_n_bits(uint8_t value, uint8_t n) override;
+  void send(uint8_t value, bool rs) override;
+};
+
+}  // namespace lcd_pcf8574
+}  // namespace esphome