🏗 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/custom/text_sensor/__init__.py

@@ -0,0 +1,29 @@
+from esphome.components import text_sensor
+import esphome.config_validation as cv
+import esphome.codegen as cg
+from esphome.const import CONF_ID, CONF_LAMBDA, CONF_NAME, CONF_TEXT_SENSORS
+from .. import custom_ns
+
+CustomTextSensorConstructor = custom_ns.class_('CustomTextSensorConstructor')
+
+CONFIG_SCHEMA = cv.Schema({
+    cv.GenerateID(): cv.declare_variable_id(CustomTextSensorConstructor),
+    cv.Required(CONF_LAMBDA): cv.lambda_,
+    cv.Required(CONF_TEXT_SENSORS):
+        cv.ensure_list(text_sensor.TEXT_SENSOR_SCHEMA.extend({
+            cv.GenerateID(): cv.declare_variable_id(text_sensor.TextSensor),
+        })),
+})
+
+
+def to_code(config):
+    template_ = yield cg.process_lambda(
+        config[CONF_LAMBDA], [], return_type=cg.std_vector.template(text_sensor.TextSensorPtr))
+
+    rhs = CustomTextSensorConstructor(template_)
+    var = cg.variable(config[CONF_ID], rhs)
+
+    for i, conf in enumerate(config[CONF_TEXT_SENSORS]):
+        text = cg.new_Pvariable(conf[CONF_ID], var.get_text_sensor(i))
+        cg.add(text.set_name(conf[CONF_NAME]))
+        yield text_sensor.register_text_sensor(text, conf)

esphome/components/custom/text_sensor/custom_text_sensor.cpp

@@ -0,0 +1,16 @@
+#include "custom_text_sensor.h"
+#include "esphome/core/log.h"
+
+namespace esphome {
+namespace custom {
+
+static const char *TAG = "custom.text_sensor";
+
+void CustomTextSensorConstructor::dump_config() {
+  for (auto *child : this->text_sensors_) {
+    LOG_TEXT_SENSOR("", "Custom Text Sensor", child);
+  }
+}
+
+}  // namespace custom
+}  // namespace esphome

esphome/components/custom/text_sensor/custom_text_sensor.h

@@ -0,0 +1,24 @@
+#pragma once
+
+#include "esphome/core/component.h"
+#include "esphome/components/text_sensor/text_sensor.h"
+
+namespace esphome {
+namespace custom {
+
+class CustomTextSensorConstructor : public Component {
+ public:
+  CustomTextSensorConstructor(std::function<std::vector<text_sensor::TextSensor *>()> init) {
+    this->text_sensors_ = init();
+  }
+
+  text_sensor::TextSensor *get_text_sensor(int i) { return this->text_sensors_[i]; }
+
+  void dump_config() override;
+
+ protected:
+  std::vector<text_sensor::TextSensor *> text_sensors_;
+};
+
+}  // namespace custom
+}  // namespace esphome