Re-enable full proguard optimization.

This is required to actually strip out log v/d calls, and the benefits
(smaller apk, fewer logs, more efficient background service) outweigh
the penalty of needing to store the mapping file.
Ignore missing translations.

This is an open-source project, and I can't demand people translate
everything. Plus, en-US has a couple further-localized strings, and
lint freaks out about this.
Code cleanup.

No optimizations or huge refactorings, yet.