Refactor naming to "GappsCheckerActivity"

Change-Id: Ieff5c44857e60971ac4efdbb65f49b55650b468d
GappsChecker: move areGappsInstalled(...) to Utils and conditionally fire the GappsCheckerActivity intent

Change-Id: I7db8d4b14046c00da6e18db292073da6458628da
GappsCheckerActivity: finish it if no notification is shown, and don't override onresume if we're not implementing our own

Change-Id: Ia41d6709c47682ba9a5f6e2980bb5c4c3bac95c4