Cache resources per-view
if following a link with get_hal encounters a PermissionDenied, hide the link.
Use ResourceCache in changesets
Add a sensible ordering to resources
ResourceCacheView now expects a user on a request; fix tests to match
Capitalize 'GDAL' properly in requirements.txt
Use ResourceCache when initially performing a changeset.
Don't perform a query if there are no resources we don't already know about.
Genericize ResourceCache to ObjectCache; add one for Source, and wrap them together
make regenerated a tuple of a path of regenerations (more correct)
Sort links so that non-stable regeneration doesn't lead to unbounded regeneration
Add debug logging to updater
Cascade resource regenerations in rounds
Cache sources when generating resources
Bulk insert identifiers when regenerating
ByIdentifierView no longer looks up sources per resource
Better separation of regeneration from saving
Let external things provide a source set for a resource; cuts down on DB queries
Rename TestCase view attribute to match naming pattern of others
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