Push notifications

This commit introduces support for push notifications.
It has been enabled for:
 * live loading of activities
 * live loading of notifications
 * live updates to content / discussion / group profile pages
 * live reloading on preview generation / new revisions
content-share only aggregates on actor
Merge branch 'push-reset' of https://github.com/simong/3akai-ux into push-reset
Follow up on push notifications
Follow up on push notifications
Issue 3429 - No unread indication when opening notification popdown
Issue 3430 - Restored revision doesn't update
Issue 3431 - format=internal is being set when subscribing for group activity feed push notifications
Follow up on push notifications code review
Followed up on code review
Followed up on code review
Issue 3432 - Notification growler not appearing with push
Issue 3433 - 2 growl notifications start appearing in the content profile when a content item I manage is commented on
Issue 3434 - Etherpad document screen refreshes every time it is published because of push updates
Clean up previous document preview styles
Remove all lazyload styles
Merge pull request #3428 from nicolaasmatthijs/push-reset

Push notifications
(Release 4.0.0) Bump version
Reorganising .travis.yml in order to have speedier builds
Merge pull request #3437 from simong/faster-travis

First attempt at reducing logging on travis and having a speedier build