Remove a bunch of unnecessary DB hits from teacherreg.

Thanks @mgersh for pointing out the repeated query.
Merge pull request #1278 from learning-unlimited/teacherreg-query-fix

Remove a bunch of unnecessary DB hits from teacherreg.
Caches EventType lookups

This kills the get_or_create for a lot of these,
but we have esp.cal.models.install() for a reason,
we should be using it.
Fixes argument name
Merge pull request #1279 from learning-unlimited/event-type-caching

Caches EventType lookups