Implemented Vertex object.
Implemented Triangle object.
Implemented Sphere object.  Changed spherical coordinates to be about the y-axis vs. the z-axis (default).
- Changed spherical implementation to be about y-axis
- Changed sphere implementation to account for a top and bottom vertex
- Added public tags to inherited classes
- Implemented basic asteroid creation (1 slice, 3 points)
- Distinguished between generic models and triangle-based models
- Implemented triangle collection as a list (<list>) versus a dynamic array
- Implemented Renderable methods