Refactor WKAoI and HUC schema definitions
Refactor WKAoI and HUC schema definitions

Since they'll be reused in the upcoming SUBBASIN_REQUEST
definition, they are pulled up into their own top-level
declarations for easier reuse.

WikiWatershed/model-my-watershed,WikiWatershed/model-my-watershed,WikiWatershed/model-my-watershed,WikiWatershed/model-my-watershed,WikiWatershed/model-my-watershed