New event system.

- First a giga-refactoring, renamed org.sofa.opengl to org.sofa.gfx,
much more adapted.
- Then completely rethought the event system to better work with touch,
mouse, pens and game controllers.
- Events are now in a spatial package org.sofa.gfx.surface.event.
- Events are not cut in two main categories: base and high-level. Base
events correspond to interactive devices events whereas high-level
events correspond to user actions.