Initial BoxGenerator implementation

The first mesh generator will generate a box.

Tasks
- [x] Add way to access strided vertex data easily. See ___List implementations. *Float32Array backend will go away once typededdata lands*
- [ ] Provide a way to access vertex data according to an input layout using the strided lists.
- [ ] Finalize the MeshGenerator base class.
- [ ] Finalize the BoxGenerator class.
- [x] Create a Mesh class that just holds the layout, VBO, and an optional IBO.
- [ ] Add hooks into the GraphicsContext to handle updated Mesh class.
- [x] Create an enumeration for primitive types.
- [x] Add an example for creating a standard mesh for use.
- [x] Create an initial implementation of the example framework which just has a way to encapsulate examples.
- [ ] Remove any obsolete methods/classes 
- [ ] Tests! Tests! Tests!