Release notes 12-16-14

@srpearce @fredsmith  @explorerleslie 

need to complete by 11:00

FYI @lamagnifica @catong 
@mhoeber I can't tell for certain if this functionality is behind a feature flag. @singingwolfboy, could you help us look at this? Is the file upload limit set for 10MB on edx.org/edge after edx/edx-platform#5731 ? @sarina 's been working with the author on this PR but she's not online right now.