NF: allow querying catalog without context of the current dataset as superdataset

[jsheunis]

i.e., search the whole catalog for records given certain query parameters, where parameter would not only be properties but also relationships (in both the parent and child direction).

From sfb1451/metadata-catalog#34

For the use case of this page being a "landing page" that was itself the entrypoint for a catalog browsing, it would be useful to

• be able to query for any use of this particular dataset version as a subdataset (and get a list of links)
• be able to query for any use of this dataset (regardless of the particular version as a subdataset (and get a list of links)