SpatialPy support

[ethangreen-dev]

• SpatialPy model to JSON support.
• Pass type of model (either GillesPy2 or SpatialPy) alongside API start job request.
• Implement run-on SpatialPy support.
• Send results back with the same kind of identification -- add some check to ensure that we don't load a SpacialPy model in GillesPy2.