Enhance GET for a simulation to include percent done

[Baguage]

From redmine, ticket 6361

Revise the GET method of Simulation resource to accept query parameter (or some flag in the request's JSON body) that indicates that the % done is to be returned if simulation's status == running model.

Note: In the OpenMalaria Portal project, Greg D has written code to parse the model's standard output to get its current percent done. See the while loop in tasks.py module -- https://redmine.crc.nd.edu/redmine/projects/openmalaria/repository/entry/WorkerPackage/Task/tasks.py#L60