Refactor GraphicContext to contain only primitive types

[obarry]

The fact that the perspective Matrix is contained in GraphicContext leads to some complexity.
In particular while updating the context or creating a new context from one of the default contexts, this implies that the perspective Matrix is sometimes created multiple times.
This can be avoided by simplifying the context to only contain the elementary data (width, height, etc.) and delegating the creation of the matrix to other party TBD and to be investigated.

[obarry]

While implementing new perspective Matrix (or matrices) for the Shadowing, this tends to confirm that the perspective Matrix could be managed in other place, may be through another class, assuming that this new class can be generic enough to be used for multipurpose including a for shadow calculation.