#54 Toggle found roms in folder

[TonyWoode]

currently for non-arcade sets, qp will display a no-rom icon for games that are missing i.e.: don't validate when the folder they're in is searched when a romdata is loaded. But we may have delibrately in this folder some subset of the roms (say we are on a portable device with less space than a non-portable device). So it would be great to be able to toggle the display of non-found roms so the folder view could just display playable games