CGame is persistent
Multi level start working

_Game is now persitent
Cameras too
When exiting a level, next one is loaded, but players are not created.
Player now survive the void beetween levels
Added a select level menu item
Put player in right position when changing level
Machine now unregister when destroyed

All elements should do this. It's the responsibility of the GameObject
script to call CElement.Destroy() when it receive the OnDestroy()
message
Merge branch 'multi-level'

Conflicts:
	Assets/Code/CGame.cs
	Assets/Code/CMachine.cs
	Assets/Code/CPlayer.cs
	Assets/Code/CScriptMachine.cs