only capture the few WIND/CAS affiliations that we care about

DMT is internal, so there's no reason to map course affiliations to Django Groups.
pull in a very simple whitelist mapper (https://github.com/ccnmtl/whitelistaffilmapper)
and configure it to only map users into the couple groups that we might
even remotely care about.
Merge pull request #77 from thraxil/no-class-affils

only capture the few WIND/CAS affiliations that we care about