testdata: add new logs with weston's upstream repaint algorithm

Alos add a contents file, so you don't need to look in git history for
descriptions.
handler: drop core_commit_damage if no output available

If the log contains a core_commit_damage event before introduction of
any outputs, we have no graph to record that event in.

Instead of crashing, just drop the event and continue.

Needed a bit of refactoring.