MOSART output scaling back using area

[changliao1025]

Some MOSART output variables should be scaled back using the cell area so they are comparable with other datasets.
For example, the total runoff can be scaled back to be compared with the forcing data.

[changliao1025]

Also the question is should we make the conversion during the save step or during the plot step.

[changliao1025]

For example, the precipitation is a flux with mass, but most time we use intensity instead of mass.
We can convert similar variables into intensity.