SD card support

[azihassan]

Since single player save files (and multiplayer stashes) are currently too large for the VMU, it would be interesting to add SD card support at least.

[AJenbo]

Since stash is a DevilutionX extension it would probably also be ok to disable the stash.

[azihassan]

Ah good point, it doesn't currently work after I flattened the paths but I'll disable it from the menu so that players don't inadvertently lose their prized possessions