Fix game mediatype extensions for vic-20
Fix game media type extensions for vic-20, so that multipart games will work properly.
The .a0 files will be detected and placed in the media browser. Any other addresses such as .20 .40 .60 .b0 are not detected, and are ignored by the media browser. However, the VIC20 emulator controller will look for these files alongside the .a0 files so that multi-part games (common for 8K and 16K cartridges) will load properly.