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