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.
add item for new edX Open Learning XML Guide.  Note something like:  This new guide is an Alpha version and is being written specifically to help those working with XML courses. edX will publish enhancements to this guide over the next several months.

link:  http://edx-open-learning-xml.readthedocs.org/en/latest/