🏗 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/sntp/sntp_component.cpp

@@ -0,0 +1,64 @@
+#include "sntp_component.h"
+#include "esphome/core/log.h"
+
+#ifdef ARDUINO_ARCH_ESP32
+#include "apps/sntp/sntp.h"
+#endif
+#ifdef ARDUINO_ARCH_ESP8266
+#include "sntp.h"
+#endif
+
+namespace esphome {
+namespace sntp {
+
+static const char *TAG = "sntp";
+
+void SNTPComponent::setup() {
+  ESP_LOGCONFIG(TAG, "Setting up SNTP...");
+#ifdef ARDUINO_ARCH_ESP32
+  if (sntp_enabled()) {
+    sntp_stop();
+  }
+  sntp_setoperatingmode(SNTP_OPMODE_POLL);
+#endif
+#ifdef ARDUINO_ARCH_ESP8266
+  sntp_stop();
+#endif
+
+  sntp_setservername(0, strdup(this->server_1_.c_str()));
+  if (!this->server_2_.empty()) {
+    sntp_setservername(1, strdup(this->server_2_.c_str()));
+  }
+  if (!this->server_3_.empty()) {
+    sntp_setservername(2, strdup(this->server_3_.c_str()));
+  }
+
+#ifdef ARDUINO_ARCH_ESP8266
+  // let localtime/gmtime handle timezones, not sntp
+  sntp_set_timezone(0);
+#endif
+  sntp_init();
+}
+void SNTPComponent::dump_config() {
+  ESP_LOGCONFIG(TAG, "SNTP Time:");
+  ESP_LOGCONFIG(TAG, "  Server 1: '%s'", this->server_1_.c_str());
+  ESP_LOGCONFIG(TAG, "  Server 2: '%s'", this->server_2_.c_str());
+  ESP_LOGCONFIG(TAG, "  Server 3: '%s'", this->server_3_.c_str());
+  ESP_LOGCONFIG(TAG, "  Timezone: '%s'", this->timezone_.c_str());
+}
+void SNTPComponent::loop() {
+  if (this->has_time_)
+    return;
+
+  auto time = this->now();
+  if (!time.is_valid())
+    return;
+
+  char buf[128];
+  time.strftime(buf, sizeof(buf), "%c");
+  ESP_LOGD(TAG, "Synchronized time: %s", buf);
+  this->has_time_ = true;
+}
+
+}  // namespace sntp
+}  // namespace esphome

esphome/components/sntp/sntp_component.h

@@ -0,0 +1,39 @@
+#pragma once
+
+#include "esphome/core/component.h"
+#include "esphome/components/time/real_time_clock.h"
+
+namespace esphome {
+namespace sntp {
+
+/// The SNTP component allows you to configure local timekeeping via Simple Network Time Protocol.
+///
+/// \note
+/// The C library (newlib) available on ESPs only supports TZ strings that specify an offset and DST info;
+/// you cannot specify zone names or paths to zoneinfo files.
+/// \see https://www.gnu.org/software/libc/manual/html_node/TZ-Variable.html
+class SNTPComponent : public time::RealTimeClock {
+ public:
+  SNTPComponent() : time::RealTimeClock() {}
+
+  void setup() override;
+  void dump_config() override;
+  /// Change the servers used by SNTP for timekeeping
+  void set_servers(const std::string &server_1, const std::string &server_2, const std::string &server_3) {
+    this->server_1_ = server_1;
+    this->server_2_ = server_2;
+    this->server_3_ = server_3;
+  }
+  float get_setup_priority() const override { return setup_priority::AFTER_WIFI; }
+
+  void loop() override;
+
+ protected:
+  std::string server_1_;
+  std::string server_2_;
+  std::string server_3_;
+  bool has_time_{false};
+};
+
+}  // namespace sntp
+}  // namespace esphome

esphome/components/sntp/time.py

@@ -0,0 +1,28 @@
+from esphome.components import time as time_
+import esphome.config_validation as cv
+import esphome.codegen as cg
+from esphome.const import CONF_ID, CONF_SERVERS
+
+
+sntp_ns = cg.esphome_ns.namespace('sntp')
+SNTPComponent = sntp_ns.class_('SNTPComponent', time_.RealTimeClock)
+
+
+DEFAULT_SERVERS = ["0.pool.ntp.org", "1.pool.ntp.org", "2.pool.ntp.org"]
+
+CONFIG_SCHEMA = time_.TIME_SCHEMA.extend({
+    cv.GenerateID(): cv.declare_variable_id(SNTPComponent),
+    cv.Optional(CONF_SERVERS, default=DEFAULT_SERVERS):
+        cv.All(cv.ensure_list(cv.domain), cv.Length(min=1, max=3)),
+}).extend(cv.COMPONENT_SCHEMA)
+
+
+def to_code(config):
+    var = cg.new_Pvariable(config[CONF_ID])
+
+    servers = config[CONF_SERVERS]
+    servers += [''] * (3 - len(servers))
+    cg.add(var.set_servers(*servers))
+
+    yield cg.register_component(var, config)
+    yield time_.register_time(var, config)