Figure out custom system/emulator icons

[rsubtil]

There are options for setting up system and emulator icons, but they don't do anything at the moment.

The reason is we need to figure out if they will be used. Currently there's no other place they show up other than the config menu, so to make them useful they should be available in other places. RetroHub may show some on it's game launched UI, but it can also be exposed to themes.

If we add custom icons, a new config folder should be made for them to store files locally.

[rsubtil]

For now, the config buttons for icons will be disabled, and this was moved to the next patch release