first commit of the final commitment: to properly handle grabbers. Just
before experimenting to remove scene.interactiveFrame()
splitting grabber pool into multiple pools and moving them to where they
belong: agents (currently called devices)
rRestoring mouse to work with single threaded timers. Remains to restore
keyboard and decide how to handle the scene actions (and maybe to
rethink how pinhole actions are handled).
Forgot to add the new classes: Duoble, EventGrabberTuplpe and KeyDuoble
Fixing all basic agents: keyboard and mouse. Remains to test space
navigator, handle low level, and build some examples