[2/2] OmniGears: task utils and navigation bar

http://jira.omnirom.org/browse/OMNI-398
http://jira.omnirom.org/browse/OMNI-345

-added switch to last app as navigation ring target
-added optional kill on long press on back

Change-Id: Ia3bed0a2f269904d8e302e75c6e64eb1cfa14663