move from ActionBarSherlock to corresponding android support lib

UI wise would makes the app compatible with android api level 7,
but other utility functions require higher level (8 for Base64 and 9 for
TimeUnit)

explicitly set the allowBackup flag and raise tested/targeted version to
api level 17

also add tool-annotations to please android-lint

Change-Id: I528e34acdeeecea6d20e8bea21b1d5c203e17c95