Add group_class attribute.
Expose generate_uuid class method, e.g., for making test fixtures.
Remove _kind columns from schema.

(Seemingly reintroduced by accident in
cc5023d40182e503e8ba109fc86e09efd6337836)
Set :null=>false explicitly on timestamp columns.

New versions of Rails do this automatically, but dev instances keep
having edit wars because some of them have never been told to add the
not-null constraint.
Add some test fixtures that are owned by folders.
Improve permission link examples.
Fill in "I'm in a folder" fixtures
Add owned_items action for groups and users.
Support limit and offset params in owned_items.
Rename include_managed to include_indirect.
Add docs for owned_items.
Add unit test for User#owned_items.
Build response objects based on item type rather than list type.
Add explanation comments to assertions.
Add tests, rename include_indirect to _linked, improve wording in
docs, improve offset/limit validation
Support filters=[["attr","=",nil]]
Rename jresponse test helper to json_response.
Merge branch 'master' of git.curoverse.com:arvados into 2640-folder-api

Conflicts:
	services/api/db/schema.rb
	services/api/test/test_helper.rb
Remove "Admin Guide" link from left nav.
Merge branch '2640-folder-api'

refs #2640

Conflicts:
	services/api/app/controllers/application_controller.rb
	services/api/config/routes.rb