Add release notes for Djblets 1.0.3.

Review Request #9587 — Created Feb. 5, 2018 and submitted — Latest diff uploaded

Information

Djblets
release-1.0.x
6432ec0...

Reviewers

This covers the changes and fixes for the avatars backend, packaging
problems, and the new enhancements for site configurations.

Built the docs. Checked that all links were correct and that there were
no build errors.

Checked for spelling errors.