Core POC support for polymer i18n (#227)

* Core POC support for polymer i18n

* Move translation from core.js to html

* Replace fetch with XHR

* Convert translation pipeline to gulp

* Convert from polyglot to Polymer localize

* Pass through missing keys for custom panels

* Store promise to be reused

* Use cacheFirst sw handler for translations

* Write full filenames to translationFingerprints

* Precache en translation

* Convert home-assistant-main to ES6 class

* Create a localization mixin

* Cleanup

* Add polymer tags to annotate for linter

* Rename fingerprints to translationMetadata

* Build translation native names into metadata

* Add language selection UI to sidebar

* Provide separate message namespace argument

* Store language/resources on hass object

* Store translationMetadata on hass

* Move language selector to config panel

* Temporarily hide language selector

* Small cleanups

* Use dynamic-align for more flexible layout

* Migrate to fetch API

* Only send change events for user selection events

* Update for new linting rules

* Migrate build_frontend changes

bower.json

@@ -9,6 +9,7 @@
   "private": true,
   "dependencies": {
     "app-layout": "^2.0.0",
+    "app-localize-behavior": "PolymerElements/app-localize-behavior#~2.0.0",
     "app-route": "PolymerElements/app-route#^2.0.0",
     "app-storage": "^2.0.2",
     "fecha": "~2.3.0",