Clean Model Wrappers

[Castronova]

Clean all of the model wrappers:

• remove unnecessary code
• eliminate dependencies on *.mdl file
• standardize the run method (i.e. run vs run_time_step)
• save function should be 'finish'

[Castronova]

Wrappers should all inherit from a single base class. Feed forward, Data, timestep should all be abstractions of this base class.

[Castronova]

simulation start and endtimes (along with other data) are hardcoded in the wrappers b/c they are read from the MDL file. This does not allow models to dynamically adjust parameters, or read them from input files.

We should try to populate this data from mdl files, but allow the model itself to override them too.

[Castronova]

general section is redundant with model