SBML timeout not supported if PyBNF installed through PyPI

[emitra17]

For enforcing the wall_time_sim for SBML models, we use a hack where the simulation is actually run in the separate script sbml-runner.py . If installing through PyPI, sbml-runner.py is not installed, so the wall_time_sim option fails

Additionally, the current error message generated for this case is not informative.

[emitra17]

#250 at least adds a useful error message. Still want to eventually fix this.

[wshlavacek]

Fixed by moving sbml_runner.py into the pybnf package and invoking it via python -m pybnf.sbml_runner. This ensures the runner script is always installed regardless of install method (PyPI or source), so wall_time_sim now works for SBML models in all cases.