Add new Material flag ColorMaterial which defines how to interpret the vertex color when lighting is enabled. It's possible to use the color for diffuse, ambient, specular, or emissive modulation. Also combined diffuse and ambient is possible. This change finally unifies the behavior of non-textured meshes in OpenGL and D3D to a large extent.

git-svn-id: svn://svn.code.sf.net/p/irrlicht/code/trunk@2350 dfc29bdd-3216-0410-991c-e03cc46cb475