CYB-253 Backend: Users should not be able to like/dislike their own work

  * totally blocks a user from liking/disliking their own work, returning 403 Forbidden
  * small refactor of spec/rails_helper.rb to add new matcher (have_return_status)

[CYB-253 Backend: Users should not be able to like or dislike their own work?](https://jira.ets.berkeley.edu/jira/browse/CYB-253)