Add release notes for Review Board 2.5 beta 1.

Review Request #6258 — Created Aug. 23, 2014 and submitted — Latest diff uploaded

Information

Review Board
master
aca1e00...

Reviewers

This adds the release notes for everything we've done so far for 2.5.
We may or may not be releasing soon, but having this typed up helps to
see where we are in the release.

Built the docs and tested the links.