first pass at version update notifications getlantern/lantern#992

goes along with getlantern/lantern@6d33036
Merge branch 'issue992/update-notifications' of https://github.com/getlantern/lantern-controller into issue992/update-notifications

* 'issue992/update-notifications' of https://github.com/getlantern/lantern-controller:
  temporary commit - @aranhoide will amend

Conflicts:
	src/main/java/org/lantern/XmppAvailableServlet.java