Release notes 12-16-14

@srpearce @fredsmith  @explorerleslie 

need to complete by 11:00

FYI @lamagnifica @catong 
I prefer your last phrasing, @catong , because it puts the focus on what the result of your action is (assign students to cohorts), instead of the mechanic by which you do it (upload a CSV file). Could you make the change?