Enable masking for polygons for seawater, glaciers, rivers, and other features

[julietcohen]

At the staging step, mask out polygons that fall over seawater, glaciers, rivers, or other features. This would be helpful for Ingmar's lake change dataset. Ingmar worked on developing this masking in his own repository. This need is also likely present for other PDG datasets, so taking care of this step in viz-staging would be ideal.

[tcnichol]

This pull request is open for filtering of seawater.
https://github.com/PermafrostDiscoveryGateway/lake_cleaning/pull/3
I had to make a few changes to get it to work, but am unable to commit, I'll sort that out when Ingmar is back.
Scripts are there for rivers as well, I'm working on checking those.