Attempting to use a react-component-like system, where the Surface simply emits everything that
happens through the shared GameUIState, and the parent (in this case the ThangsTabView, but theoretically
anything that uses the surface) handles the events manually, to enforce desired behavior for that particular
context.
It's nice that all the event handling is centralized, but it's still a bit of a mess, and not thoroughly
stateful. But it's a start. This is in preparation for allowing multi-thang selection and manipulation
in the level editor.
