Add BRANCH to Accepted and Needs Revision e-mails

Summary:
I always forget a branch which I used for the diff so that I must open
my browser which takes some time. This diff adds the name of the branch to the
sent e-mails. But only if the diff is in the state Accepted or Needs Revision to
not pollute other e-mails.

Test Plan:
Comment
Request changes
Accept
Look at the e-mails

Reviewers: epriestley

Reviewed By: epriestley

CC: olivier, aran, epriestley, vrana

Differential Revision: https://secure.phabricator.com/D1396