Enable wrapping to first/last page in file browser

This enables wrapping to the first/last page (or the first/last item, if it's only one page) when you press down/up in the file browser.

I thought about making it do it when you press right/left too, but i think it might be too easy to accidentally wrap around when you're paging through. That's probably why some other menu systems, like MiSTer's, only do it with down/up.

This does make the file browser work a bit differently from the other menus, though. If you like, i can do the same thing with those. Let me know how you feel

PS: Thank you for the file sorting. I'd just assumed there wasn't enough RAM for it; pretty happy that's not the case