Output gdat file for best fit

[emitra17]

Requested by Bill.

Currently I think this is only done if delete_old_files = 0 so the gdat file is already available.

[emitra17]

Two ways to do this:

1. Don't delete the simulation folder of the best run, so the gdat file is available - Annoying bookkeeping; potentially adds another requirement to Algorithm subclasses; wouldn't work for SBML models.
2. Run the model again at the end of the run - More straightforward to implement. But you wouldn't always want this - if your model has a long run time and your run is on a cluster, it's a waste of parallel resources.

[emitra17]

Bill says it's an acceptable compromise have a config option to activate option 2 above, with default being disabled.