GPII-368: Adds the ability to install the GPII apk in /system/app

This pull request should be the final piece in the puzzle of "making it work" on Android. We'll need to update some of our documentation, too, which I can do once this passes code review and gets in.

@javihernandez or @sgithens, can one of you review this and share your feedback? I'm not exactly an elite bash coder, so there may be some rough edges here. Let me know what you think.