CYB-272 Item submitter gets points when another user comments on item

  * Returns HEAD 201 CREATED when a comment is created, whether or not
    the comment poster is credited points (done only if not the original poster).
  * Returns HEAD 204 NO CONTENT when a comment is updated.

[CYB-272 Item submitter gets points when another user comments on item](https://jira.ets.berkeley.edu/jira/browse/CYB-272)