Remove event handling from the cameras.

At the moment event handling is exclusively done by the active camera. This is not very modular since event handlers could be stand-alone controllers that modify some scene node properties.

No files or tests are named. Start by locating the active camera's event-dispatch path and how handlers update scene-node properties. Done means event handling is no longer exclusively owned by the active camera and standalone controllers can modify scene nodes.

Written by the indexing model from the issue text.