Commits building up to the refactored UI

This pull request consists of a series of commits that build up to the fully refactored version of AppRTC as at [apprtc-m.appspot.com](https://apprtc-m.appspot.com).

The first commit is a minimal version of the new UI without any of the following: 
· analytics
· header/icons
· camera change
· sharing (except link)

Each subsequent commit will add these features.

nit: top/bottom and left/right values are the same, so should be:
margin: 0 auto;