Camera:  Enhance camera movement.

WASD: Used to rotate camera.
UP-DOWN-RIGHT-LEFT arrows: allows to move forward backward, left and right.
Move forward towards where you are looking. along z and x axis.
TODO: Allow movement towards y-axis.
Mesh Loader: Bug fix when a triangle is a line.

When triangle is a line, it isn't possible to compute a normal.  A normal of
(0, 0, 0) will therefore be affected.
When no normals are defined, we compute them, otherwise we use the defined
normals from file.
TODO No normals and no textures, Nothing is done.
TODO:  Adding a TODO list.