[1/2] base: add switch to last app as navigation ring target

This commit actually includes the long press back button to kill an app, but i only want the last app on nav ring

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

PS2
much easier :)

PS3
whitespaces

Change-Id: I31f11fcd0efb90f007017fa16567e6711002ecc8