integration of event display ongoing

Not functionnal so far. geometry.C still only displays the geometry in a
eve window.
Almost integrated geometry and event display

In terms of functionalities, we should be close. But this has to be
debugged. Then, other features will have to be developed.
Mostly in place but crashing

Just debugged the obvious typos and other things. It compiles.
Still, crash at runtime in TGeoManager::SetTopVolume(TGeoVolume*)
First working version

Many features are still missing, but that version provides the minimal
features in EventDisplay and in addition: event control and transluscent
geometry.