Support multi-side and multi-disk FDS games
Migrated from https://bugzilla.gnome.org/show_bug.cgi?id=781690
Many FDS games use the two sides of the disk, we should allow to flip it.
It is currently possible to do now by pressing Q key, but not possible with GUI.
An example of a game that absolutely requires this: Japanese version of Castlevania 2. Create a player, start game and it requests flipping the disk.