Show whether a related change is merged or old.

Include a colored circle at the end of the related change line to
indicate the state. Use a black circle when the change is a link to
gitweb and a orange circle when the link to the change is not the
current patch set. Expose the current_revision_number on the
ChangeAndCommit object.

Change-Id: I5c629ecac61a4b9c6fc709f328a290313e3d6093