Fix bug in spam blocking

Editing a comment such that it matched a blocked hash would cause the
API to return 503 but actually update the comment. This is now fixed.
Fix a bogus test
Add thread type feature

There are two thread types, discussion and question. Discussions have
the same behavior that current threads do. When a question is returned
from the API, it contains separate fields for its endorsed and non-
endorsed entries.

Co-authored-by: Jim Abramson <jsa@edx.org>
Merge pull request #108 from edx/gprice/thread-type

Add thread type feature
Add/update thread filters (flagged, unread, unanswered).
Merge pull request #112 from edx/jsa/thread-filters

Add/update thread filters (flagged, unread, unanswered).