* Update frontend
Conflicts:
homeassistant/components/frontend/version.py
homeassistant/components/frontend/www_static/core.js.gz
homeassistant/components/frontend/www_static/frontend.html
homeassistant/components/frontend/www_static/frontend.html.gz
homeassistant/components/frontend/www_static/home-assistant-polymer
homeassistant/components/frontend/www_static/service_worker.js
homeassistant/components/frontend/www_static/service_worker.js.gz
* Add a default OPTIONS handler for wsgi (#2301)
When a browser makes a CORS request, it often makes a 'preflight'
options request in order to make sure the resource is valid, and that
it has the right CORS access. This adds a default OPTIONS handler for
all views. If a view needs to customize the OPTIONS handler for some
reason, it's free to, but this way CORS will work.
* Version bump to 0.21.2