Separate geometry (attributes) from Model

[ibgreen]

Our model knows how to combine programs (shaders), attributes and uniforms.

It is also the base class for our geometric primitives (planes, cylinders, spheres etc). But geometric primitives are typically only a set of attributes and some props like drawType.

A separate geometry or attributes class that can be installed on a Model might be a more flexible setup, that would allow the overly broad Model class to become more focused.

Also compare attributes.js in deck.gl performance branch, it could be a good base for a geometry/attributes class.

@mikolalysenko

[ibgreen]

This is implemented on dev branch