[WIP] ADD: [droid] Hide action bar during video playback

As https://github.com/xbmc/xbmc/pull/2091 seems to be stale, this one follows it up, adapted to latest changes (min api 14, main.java, ...)

There is still an issue:
When the nav bar is hidden, a touch shows it up but we don't get the touch event, so you actually have to touch twice to get the OSD.