Tier 3 USGIN OGC Services

Frontend:
-Removed `Download` option from tier 3 services and replaced it with `GetCapabilities`.
-Removed publish OGC popup form for tier 3 services; not necessary because files have already passed validation.
-Routed a new action for dealing with tier 3 data.

Backend:
-Object in content models 'extension' which tells Geoserver 'extension' how to handle tier 3 data.
-New action for using object.
-Changed a bunch of those helper dialogues for OGC services.

Also, took this as an opportunity to start abstracting some things in the Geoserver extension:
-Default information about workspaces/datastores/namespaces is set in configuration file (before it was all just 'ngds')
-If user doesn't want to use defaults, they simply pass in a Geoserver object for the workspace/datastore/namespace they'd like to use instead.