🏗 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/max31855/max31855.cpp

@@ -0,0 +1,91 @@
+#include "max31855.h"
+#include "esphome/core/log.h"
+
+namespace esphome {
+namespace max31855 {
+
+static const char *TAG = "max31855";
+
+MAX31855Sensor::MAX31855Sensor(const std::string &name, uint32_t update_interval)
+    : PollingSensorComponent(name, update_interval) {}
+
+void MAX31855Sensor::update() {
+  this->enable();
+  delay(1);
+  // conversion initiated by rising edge
+  this->disable();
+
+  // Conversion time typ: 170ms, max: 220ms
+  auto f = std::bind(&MAX31855Sensor::read_data_, this);
+  this->set_timeout("value", 220, f);
+}
+
+void MAX31855Sensor::setup() {
+  ESP_LOGCONFIG(TAG, "Setting up MAX31855Sensor '%s'...", this->name_.c_str());
+  this->spi_setup();
+}
+void MAX31855Sensor::dump_config() {
+  LOG_SENSOR("", "MAX31855", this);
+  LOG_PIN("  CS Pin: ", this->cs_);
+  LOG_UPDATE_INTERVAL(this);
+}
+float MAX31855Sensor::get_setup_priority() const { return setup_priority::DATA; }
+void MAX31855Sensor::read_data_() {
+  this->enable();
+  delay(1);
+  uint8_t data[4];
+  this->read_array(data, 4);
+
+  // val is 14 bits of signed temperature data followed by 2 bits of status flags
+  int16_t val = data[1] | data[0] << 8;
+
+  // test data from MAX31855 datasheet
+  // val = 0x6400 // 1600.00°C
+  // val = 0x3E80 // 1000.00°C
+  // val = 0x064C // 100.75°C
+  // val = 0x0190 // 25.00°C
+  // val = 0x0000 // 0.00°C
+  // val = 0xFFFC // -0.25°C
+  // val = 0xFFF0 // -1.00°C
+  // val = 0xF060 // -250.00°C
+
+  this->disable();
+  if ((data[3] & 0x01) != 0) {
+    ESP_LOGW(TAG, "Got thermocouple not connected from MAX31855Sensor (0x%04X) (0x%04X)", val, data[3] | data[2] << 8);
+    this->status_set_warning();
+    return;
+  }
+  if ((data[3] & 0x02) != 0) {
+    ESP_LOGW(TAG, "Got short circuit to ground from MAX31855Sensor (0x%04X) (0x%04X)", val, data[3] | data[2] << 8);
+    this->status_set_warning();
+    return;
+  }
+  if ((data[3] & 0x04) != 0) {
+    ESP_LOGW(TAG, "Got short circuit to power from MAX31855Sensor (0x%04X) (0x%04X)", val, data[3] | data[2] << 8);
+    this->status_set_warning();
+    return;
+  }
+  if ((data[1] & 0x01) != 0) {
+    ESP_LOGW(TAG, "Got faulty reading from MAX31855Sensor (0x%04X) (0x%04X)", val, data[3] | data[2] << 8);
+    this->status_set_warning();
+    return;
+  }
+
+  if ((val & 0x8000) != 0) {
+    // Negative value, drop the lower 2 bits and explicitly extend sign bits.
+    val = 0xE000 | ((val >> 2) & 0x1FFF);
+  } else {
+    // Positive value, just drop the lower 2 bits.
+    val >>= 2;
+  }
+
+  float temperature = float(val) / 4.0f;
+  ESP_LOGD(TAG, "'%s': Got temperature=%.1f°C", this->name_.c_str(), temperature);
+  this->publish_state(temperature);
+  this->status_clear_warning();
+}
+
+bool MAX31855Sensor::is_device_msb_first() { return true; }
+
+}  // namespace max31855
+}  // namespace esphome

esphome/components/max31855/max31855.h

@@ -0,0 +1,27 @@
+#pragma once
+
+#include "esphome/core/component.h"
+#include "esphome/components/sensor/sensor.h"
+#include "esphome/components/spi/spi.h"
+
+namespace esphome {
+namespace max31855 {
+
+class MAX31855Sensor : public sensor::PollingSensorComponent, public spi::SPIDevice {
+ public:
+  MAX31855Sensor(const std::string &name, uint32_t update_interval);
+
+  void setup() override;
+  void dump_config() override;
+  float get_setup_priority() const override;
+
+  void update() override;
+
+ protected:
+  bool is_device_msb_first() override;
+
+  void read_data_();
+};
+
+}  // namespace max31855
+}  // namespace esphome

esphome/components/max31855/sensor.py

@@ -0,0 +1,21 @@
+import esphome.codegen as cg
+import esphome.config_validation as cv
+from esphome.components import sensor, spi
+from esphome.const import CONF_ID, CONF_NAME, CONF_UPDATE_INTERVAL, \
+    ICON_THERMOMETER, UNIT_CELSIUS
+
+max31855_ns = cg.esphome_ns.namespace('max31855')
+MAX31855Sensor = max31855_ns.class_('MAX31855Sensor', sensor.PollingSensorComponent, spi.SPIDevice)
+
+CONFIG_SCHEMA = cv.nameable(
+    sensor.sensor_schema(UNIT_CELSIUS, ICON_THERMOMETER, 1).extend({
+        cv.GenerateID(): cv.declare_variable_id(MAX31855Sensor),
+        cv.Optional(CONF_UPDATE_INTERVAL, default='60s'): cv.update_interval,
+    }).extend(cv.COMPONENT_SCHEMA).extend(spi.SPI_DEVICE_SCHEMA))
+
+
+def to_code(config):
+    var = cg.new_Pvariable(config[CONF_ID], config[CONF_NAME], config[CONF_UPDATE_INTERVAL])
+    yield cg.register_component(var, config)
+    yield spi.register_spi_device(var, config)
+    yield sensor.register_sensor(var, config)