primarily performance and correctness lint fixes

This is a long one, but it takes care of a decent amount of annoyingness and makes our code more obvious and explicit. Also cleaned up unused resources that have been sitting around for quite a while.

Performance improvements are largely around flattening layouts and minimizing memory leaks, correctness about hardcoded strings and explicit annotations for using APIs only available on certain platforms.
We can probably go ahead and put ourselves squarely in the gradle world now?