Watershed: inclusive/exclusive

[gassc]

Need to be able to specify the scope of the watershed function:

• "culvert approach": watershed delineation from input points is inclusive - downstream catchments include upstream catchments
• "catch basin approach": watershed delineation from input points is exclusive - no catchment overlap (this is the default way the watershed delineation function works)

[gassc]

To do a truly exclusive model on a subset of inlets, we will need to generate a complete watershed raster with all other inlets in the basin first. There's really no way around that, as the watersheds of those other inlets define the watershed of any inlets of interest.

Then, with that watershed, we can use the initially selected inlets to select only the corresponding zones in the watershed, and proceed from there.

[gassc]

This really just represents differing ways to use the tool, and both ways work in the tool's current form. We'll add documentation explaining the different approaches.