Calculation of Face Flow and Cell Volume

[sjordan29]

The model that we worked with for all of our testing had both face flow and cell volume printed to output (by default, this information is NOT printed, but we turned it on). If those values are not included, the face flow and cell volume should be calculated by the Clearwater Riverine model.

However, in some recent testing with a different model, @jrutyna found that there were errors thrown when the the face flow and cell volume outputs were not turned on. Therefore, this error handling and/or calculation is not properly implemented and should be addressed.