Hacked in some scrolling support.

This was mainly just to get a feel for how key events are routed by JavaFX. Now
I need to think about and implement more civilized key map support as well as
the basic "interactive action" framework.
Starting on strawman API/impl breakdown.

The core of the editor will be as simple as possible, and the vast majority of
functionality will be "stock" extensions written against the public API.