click nickname to start a call

- basic RTC object
- click on a username to initiate a call
- new CallView to display the user's video

Quite much a work in progress
added UserEntryView and VideoView
added video controls
preparing layout and VideoView for rtc connexions
sync with master
added user icons in connected people list
sync with master
added events for sign in & sign out
Merge branch 'initiate-a-call' into rtc
externalized stylesheet