Cleans up path centering logic.

Squashed commit of the following:

commit dc5bedb4cc76a36c0cded41f0d45afa6e9fb0ac3
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Sun Jul 27 15:09:20 2014 -0500

    Rebuilds app.js.

commit 67980d4e0196aeb34557a32332f4ece31dad8e94
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Sun Jul 27 15:00:22 2014 -0500

    Scopes path centering to be local to the actor, rather than global.

commit 28845f6fbe66336c58fbdd1646c5a9f1d5ab30d1
Author: Jeremy Kahn <jeremyckahn@gmail.com>
Date:   Sun Jul 27 11:53:32 2014 -0500

    Cleans up event handling a bit.