Adds an encdec module.

Adds the encdec module privoding the EncodeDecode object. This baseclass
will be reponsible for providing a consistent to-JSON and from-JSON API.
Large API changes.

Adapts code to use the new encdec interface. Improves SBK file support
to use JSON format, with base64/zlib encoding for large data. Changes
bounds min/max to vec3 types. Removes the old create_wireframe and
get_attribute methods. Finally, breaks the Model interface into
consistent Model/Mesh objects.