Offer a warning about using nightlies to users.

Patchset 1) intial commit
Patchset 2) - modified strings
            - new updateUpdatesType() function
            - cancel option on dialog
            - updated AlertDialog style to better match
              other userse in CMUpdater
            - misc clean up
Patchset 3) minor cleanups
Patchset 4) String changes

Change-Id: Ib7d215702b7035c615ea6ef3dfd09610d2d3a5d1