Improve disc load/save UI/UX

[mattgodbolt]

Lots of issues:

• no way to know which disc is currently loaded in each drive
• awkward menu setup to load them in the first place
• no way to "unload" a disc
• weird partition of "examples or local" vs "from stairway to hell" to GDrive to whatever. Users have to kinda guess where to load things.

Should probably think about how this fits into a more general peripheral config, as tapes have a similar problem/ux issue.