Draft of release notes for 10-7

@lamagnifica @mhoeber @explorerleslie Please review. (Leslie - in particular, can you review the bullets that have to do with discussions?) Built version at http://draft-107-release-notes.readthedocs.org/en/latest/10-07-2014.html.
I'd add a line something like - we encourage course staff to point students to this document as needed, and to let edX know of other student needs and questions that are not yet addressed.  (since students won't likely find by themselves right now)