write a spec or doc for the swap feature

[hcientist]

1. can't always swap
   1. if there are too few students in the course || too few authors of the current prompt, can't swap
2. when swapping: don't give author one of their own thoughts, if one author is more prolific for a certain prompt, before assigning all their thoughts to others, first ensure that each author's thoughts are assigned (and specifically to authors (users who have submitted for this prompt))