Update the URL to the new android mobile client
First changes for the new logic when joining via mobile

There will be a single button to join a conference. If the user is in a mobile
device, the mobile client will be automatically triggered. The old modal window
to join via mobile was removed.

Made a new "mobile" layout, currently only used in the page shown to join a
conference from a mobile client, but that can be used for more in the future.
Update bigbluebutton_rails and automatically join via the mobile app

refs #1247
Use an icon to identify the dropdown button with webconf options
Remove device options from the invite view

Now there's no need to selected if joining from a mobile or desktop, since
the join action will do it automatically.
So the invite view now only confirms the user name and asks for a password
(for private rooms).

refs #1247
Merge branch 'branch-v2' into branch-v2-mobile

Conflicts:
	Gemfile
	Gemfile.lock
	app/assets/stylesheets/app/application/base.css.scss
	app/helpers/custom_bigbluebutton_rooms_helper.rb
Merge remote-tracking branch 'origin/branch-v2-mobile' into branch-v2
bigbluebutton_rails back to branch master