🏗 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/template/text_sensor/__init__.py

@@ -0,0 +1,42 @@
+from esphome.automation import ACTION_REGISTRY
+from esphome.components import text_sensor
+from esphome.components.text_sensor import TextSensorPublishAction
+import esphome.config_validation as cv
+import esphome.codegen as cg
+from esphome.const import CONF_ID, CONF_LAMBDA, CONF_NAME, CONF_STATE, CONF_UPDATE_INTERVAL
+from .. import template_ns
+
+
+TemplateTextSensor = template_ns.class_('TemplateTextSensor', text_sensor.TextSensor,
+                                        cg.PollingComponent)
+
+CONFIG_SCHEMA = cv.nameable(text_sensor.TEXT_SENSOR_SCHEMA.extend({
+    cv.GenerateID(): cv.declare_variable_id(TemplateTextSensor),
+    cv.Optional(CONF_LAMBDA): cv.lambda_,
+    cv.Optional(CONF_UPDATE_INTERVAL, default='60s'): cv.update_interval,
+}).extend(cv.COMPONENT_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 text_sensor.register_text_sensor(var, config)
+
+    if CONF_LAMBDA in config:
+        template_ = yield cg.process_lambda(config[CONF_LAMBDA], [],
+                                            return_type=cg.optional.template(cg.std_string))
+        cg.add(var.set_template(template_))
+
+
+@ACTION_REGISTRY.register('text_sensor.template.publish', cv.Schema({
+    cv.Required(CONF_ID): cv.use_variable_id(text_sensor.TextSensor),
+    cv.Required(CONF_STATE): cv.templatable(cv.string_strict),
+}))
+def text_sensor_template_publish_to_code(config, action_id, template_arg, args):
+    var = yield cg.get_variable(config[CONF_ID])
+    type = TextSensorPublishAction.template(template_arg)
+    rhs = type.new(var)
+    action = cg.Pvariable(action_id, rhs, type=type)
+    template_ = yield cg.templatable(config[CONF_STATE], args, cg.std_string)
+    cg.add(action.set_state(template_))
+    yield action

esphome/components/template/text_sensor/template_text_sensor.cpp

@@ -0,0 +1,25 @@
+#include "template_text_sensor.h"
+#include "esphome/core/log.h"
+
+namespace esphome {
+namespace template_ {
+
+static const char *TAG = "template.text_sensor";
+
+TemplateTextSensor::TemplateTextSensor(const std::string &name, uint32_t update_interval)
+    : TextSensor(name), PollingComponent(update_interval) {}
+void TemplateTextSensor::update() {
+  if (!this->f_.has_value())
+    return;
+
+  auto val = (*this->f_)();
+  if (val.has_value()) {
+    this->publish_state(*val);
+  }
+}
+float TemplateTextSensor::get_setup_priority() const { return setup_priority::HARDWARE; }
+void TemplateTextSensor::set_template(std::function<optional<std::string>()> &&f) { this->f_ = f; }
+void TemplateTextSensor::dump_config() { LOG_TEXT_SENSOR("", "Template Sensor", this); }
+
+}  // namespace template_
+}  // namespace esphome

esphome/components/template/text_sensor/template_text_sensor.h

@@ -0,0 +1,27 @@
+#pragma once
+
+#include "esphome/core/component.h"
+#include "esphome/core/automation.h"
+#include "esphome/components/text_sensor/text_sensor.h"
+
+namespace esphome {
+namespace template_ {
+
+class TemplateTextSensor : public text_sensor::TextSensor, public PollingComponent {
+ public:
+  TemplateTextSensor(const std::string &name, uint32_t update_interval);
+
+  void set_template(std::function<optional<std::string>()> &&f);
+
+  void update() override;
+
+  float get_setup_priority() const override;
+
+  void dump_config() override;
+
+ protected:
+  optional<std::function<optional<std::string>()>> f_{};
+};
+
+}  // namespace template_
+}  // namespace esphome