back button for touch mode

[da-anda]

As Kodi is running in fullscreen mode on Android, there is no back button visible by default. To get the OS back button, you have to swipe up from the bottom. Doing so, I almost always hit something within Kodi (or any other app) which really sucks. Therefor it would be nice to have a dedicated back button in touch mode. Maybe ditch the fav icon for that, as I don't think it's something you really need at hand on every screen.