Add references to work branch in PR

[zanerock]

Overview

Let's remember the work branch and the final pre-merge branch in the PR description.

Deliverables

• Add 'Workbranch: XXX (YYY)', where X is the branch name and Y is the first 6 digits of the rev hash; right below 'Submitted by'
• Make that a link pointing to the repo on github at the final pre-merge commit point.
• Add a comment with the final merge commit rev as a link to the repo on github at that point.