Fix check and show answer for split

LMS-11237

@cpennington I had to impl resources_fs in split b/c capa_problem accesses it. imnsho, we should review all filesystem stuff. Anyway, my concern was using the course as the subdir could cause collisions w/ other == named courses, but that should be a current problem too; so, it's probably ok?

Given that we're trying to support reruns of the same course, I think it would be better to use org, course, and run in the directory path, if possible.