Implementation of HDS in SUMMA

[MIsmlAhmed]

This is the initial implementation of the Hysteretic Depressional Storage (HDS) algorithm for prairie potholes in the SUMMA model.

The model has been tested under different I/O configurations and works as expected on a hypothetical test case.

To activate the HDS model, the following has to be done:

1. a model decision must be defined to activate HDS as:

   prPotholes HDSmodel ! (39) choice of prairie pothole representation

2. The following HDS parameters must be defined at the GRU (basin) level in the zParamTrial.nc file (if the parameters are spatially variable) or in theBasinParamInfo.txt if they are spatially constant. The following is an example of dummy parameters value.

4. At least one initial condition needs to be defined pondVolFrac at the GRU level in the zInitialCond.nc

[MIsmlAhmed]

@martynpclark, please review this. I can't add you as a reviewer to this PR because I don't have permission.

[MIsmlAhmed]

I can include the test step I have been experimenting with (if that's helpful).