Use bulk_create in add_default_permissions() to speed up unit tests
Make Plot's CRUD operations work for other map features
Add CRUD endpoints for features

Also:
* (most of the changes), use "feature_id" instead of "plot_id" in view funcs and URL matching
* Organize plot/feature URLs a little better, and add names for URLs that lack them
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Merge pull request #1064 from RickMohr/crud_map_features

Add CRUD operations for map features