* Added InstancedNode: easy to use instancing with similar API to BatchNode. The underlying scene graph will be automatically optimized so instancing is used as much as possible, thus reducing number of draw calls and improving performance. Unlike BatchNode, it does not copy the geometry's mesh around, but only its transform. In order for it to work, it requires the Renderer to support the GeometryInstancing capability.
 * Replaced existing instancing test with TestInstanceNode, which demostrates how to use the new InstancedNode by changing the transform, mesh, and material of every instance periodically.
 * The lower-level InstancedGeometry API rewritten: Users don't need to manage the number of instances they have and their indices. Instead, they can use addInstance() and removeInstance() to add and remove instances as desired. Unlike InstancedNode, InstancedGeometry requires all Geometries to have the same mesh and material, but they can have different transforms.
 * Instancing.glsllib now requires the InstanceData to have world transforms instead of world view transforms. As a consequence, users of instancing must specify in the material the world parameters ViewProjectionMatrix and ViewMatrix instead of ProjectionMatrix.