Math functionality expanded.

Angle structure is now used whenever angles are defined. Rotation for
vectors is now simplified (although some tests should be performed).
Transform object now defines a scale vector, and not just a scale
number.
Mouse events added

Scrolling and mouse buttons clicking handled by the Game instance.
Still, neither scrolling nor other mouse events are used by the
rendering engine.
New constructor added to Quaternion class
Cameras will become game components.

Prepared the rendering engine to handle the cameras as game components.
Camera is now a part of the scene graph

Camera now is a game component.
Scene graph extended with cameras. Works now!

Scene graph can now define cameras and the rendering engine makes use of
these new game nodes.
Camera position and rotation handled.

Camera game node can now be moved and / or rotated by the user using the
keyboard.
Transform hierarchy. Math testing project added.

Transform hierarchy functionality created, but still to be tested and
checked. Now, game nodes may define its transformations relatively to
their parent transformation. New math testing project added to the whole
solution. First two tests are added to this new project.