3072: add an empty collection in db seeds

Added empty collection (owned by the anonymous group) to test fixtures
and to db/seeds.rb.

API integration tests: in permissions_test.rb, test that the active user
can read objects in the anonymous group, even when there are no explicit
permission links on that group or objects in it.

Workbench integration tests: added a test to confirm that a non-admin
user can get the empty collection.

Cleanup code: User.can? now takes either a uuid or an object for the target.

Refs #3072.
3072: anonymous group can_read empty collection

empty_collection is owned by the system user, like all other
collections. When it is created, a permission link is also created
giving the anonymous group permission to read it.

Added test fixtures for the empty collection and its associated
permission link.

Workbench renders links to the empty collection as "Empty Collection".

The unit test and integration tests focus just on the empty
collection (other collection ownership/readability issues will be
addressed elsewhere).
3072: rendering "Empty Collection" in default_name

Collection.default_name now renders "Empty Collection" for collection
d41d8cd98f00b204e9800998ecf8427e.

Refs #3072.
Merge branch '3072-empty-collection-bugfix'

closes #3072.