Added component wise multiplication for Vectors
Changed the intersection interface

From now on, the system does not save all the intersection that were created.
Instead, only the best intersection is carried through all the computations.
This makes the code easier, since we do not intend to use the other
intersection further down the ray.
Adapted the SimpleGroup to the new interface
Adapted the Disc to the new interface
Adapted the InfinitePlane to the new interface
Adapted the Sphere to the new interface