[Android] Overlay now works during emulation.
[Android] General cleanup.

We no longer need the buttons in Assets, considering they are now resources (ie. drawables).

Also remove (now) junk code from VideoSettingsFragment.java. We handle the input overlay within the InputSettingsFragment.

Also add a TODO detailing what needs to be refactored when axis support is finally added.
[Android] More cleanup. We don't need the preference to enable/disable the overlay in the video preferences anymore.