OR-454 Add the number of unread TimelineEntries in the left widget.

* Remove `.leftPane` css
* Add `esn.communityAStracker` module in the app.js
* Add the js controller script in `index.jade`
* Add the new element `list-community-activity-streams` in the
`application.jade` in the left widget
* Add the view and the controller for the community activity stream
tracker (which manage the number of unread TimelineEntries)
OR-454 Add unit frontend tests
Merge pull request #330 in OR/rse from ~RPIGNOLET/rse:OR-454 to master

* commit 'c90d0a7ee1f8cac07d83e62b4b5242d96863d3af':
  OR-454 Add unit frontend tests
  OR-454 Add the number of unread TimelineEntries in the left widget.