ChangeScreen2: Display 'No Related Changes' if there are none

Instead of returning ourselves as the only result from /related
return an empty list. This is more clear to the caller that there
are no related changes for the searched for change.

In the web UI display a message making it clear there are no
related changes.

Change-Id: Icccd2fbb9d6b21965e699060228a108a83b22838
3 files changed