Make branch columns link to changes on that branch

Similar to what we do with the project column, link the branch name
in the branch column to all changes that match that branch, and the
topic field to changes matching the topic.

Bug: issue 509
Change-Id: I9f7c4702c3dde1704ea5a935fcbea3e478108179
Signed-off-by: Shawn O. Pearce <sop@google.com>
3 files changed