Added release notes for Review Board 2.5.17.
Review Request #997 — Created Dec. 7, 2017 and updated
This is a small bug fix release that fixes some compatibility problems with GitLab and LDAP, along with bugs with file attachments and floating draft banners for replies, e-mail headers, and a query. Testing Done: Built the docs and looked through them. Checked for spelling and build errors. Reviewed at https://reviews.reviewboard.org/r/9423/