Allow the app to run on new tickets + listen for subject changes

Hi guys,

The app could not run on new tickets since `ticket.id` was a required property. I removed this requirement and added a listener for the `ticket.subject.changed` event as well so that the app would redo the search upon subject change.

Here's a small demo of the new behavior:
![related ticket](https://f.cloud.github.com/assets/330573/2460245/07865598-af68-11e3-9974-2eb0d447c1cc.gif)
Let me know if you want me make other changes,

Cheers,

Pierre.