Support SDK Version >=7, and assorted cleanups

Hi Michael,

I'm particularly interested in seeing the minSdKVersion change go in, since I have an app (https://github.com/nikclayton/android-squeezer) that supports SDK 7 and up and I'd like to use the ColorArt library with it.  As far as I can tell there's nothing in ColorArt that uses any higher SDK features, so this should be safe.

The other changes are just straightforward cleanups.

Thanks, Nik