Added dualshock 4 gamepad type, and implemented very basic fullscreen. We still have no proper designs for fullscreen (in GNOME in general), so it's more or less what the old app was doing (based on the ephy code). Not great, but enough for now ig.
Note that it doesn't remember fullscreened state, so it can be used on phosh without softlocking the app. (the fact I need to mention that is one of the reasons the current fullscreen is a mess)
Two more things:
- There's now a basic gamepad navigation. It's possible to browse the library, run games and exit them
- Fullscreen state is now remembered
- For secondary window for Nintendo DS, the monitor is remembered too for fullscreen, so if you have two screens, you can fullscreen it on a secondary monitor and it will stay there next time
With this the app can now be used on, say, TVs :3
