Fix saving/loading badge designs with backgrounds

This removes saving/loading of the studioBackground badge field when designing badges.  It was still assuming the old system of using static backgrounds from a list of backgrounds provided by the server, as opposed to the new system of user-uploaded backgrounds.

This fixes the errors associated with saving or opening the designer for badges with backgrounds, but it does not fix the issue of backgrounds not being saved.  Thus, if you reopen the designer for a badge that has an uploaded background, it will not have the previously uploaded background as an option in the designer.  This will be done in a separate PR.