Ref #496. Fixed a few issues with the evaluations module. Firstly, made sure the organisation ID sticks around when editing questions of the rubric type (and that it doesn't change to the user's current organisation rather than staying at what the question was initially, for all question types), then also made the descriptors api call fail more gracefully if no descriptors exist- while adding in some defaults to the database as well, and finally, removed the requirement for a "request" to exist for evaluations with them enabled, unless it is explicitly required.