Related to http://roadmap.highfidelity.com/open-source-project-proposals/p/procedural-materials-on-models-and-avatars

Allow Procedurals to specify a custom vertex shader. If an entity has a procedural vertex shader, it should get its bounding box from the material entity.

Part of this work was done here, but it needs to be redone and allow the material entity to specify the render bounds: https://github.com/highfidelity/hifi/pull/13823