Primitives: fixed include guard.
Primitives: no need to have this stuff public.
Primitives: wireframe versions of Capsule, Cylinder and UVSphere.

Simplified representation of the shapes, i.e. an UVSphere is
visualized by three circles, one for each axis. Will be used mainly in
DebugTools.
DebugTools: implemented ShapeRenderer for 3D sphere.
Initial support for OpenGL 4.4.
Assert instead of returning empty list in Context::supportedExtensions().
Support for ARB_texture_stencil8.