Import non-Wheel Witch saves

[skiletro]

Raised from #33, it would be nice if the user could import their external Retro Rewind save data into the app (rksys.dat, rrating.pul, etc) from users who previously had the game installed manually, and have the app copy over the files to the appropriate locations.

[matellush]

The RRRating.pul file should be already available as it is in the Wii subfolder (unless it is being imported from a Wii's SD card, in which case it would be in the SD card's RetroRewind6 folder, as would be the case with ghost data in RetroRewind6/Ghosts...). For the RetroWFC rksys.dat files, I would maybe suggest an option to scan the entire Dolphin tree for save/RetroWFC or save/RetroWFC2 (depending on the separate savegame option) directories and letting the user select which directory to import into the WheelWitch/pack/riivolution/save/RetroWFC directory (Wheel Witch itself does not use RetroWFC2).

While this would only scan for saves in the Dolphin user folder, this would already be an improvement. Importing external save files would be an additional issue.