Support lists of values in query filters

[apdavison]

Currently, passing a list of values as a filter does not work. For example:

omcore.SoftwareVersion.list(client, developers__family_name=["Baggins", "Oakenshield"])

sends the list as the value of a single filter, which the KG rejects with a 500 error, and a list of linked objects (e.g. Chapter.list(client, authors=[p1, p2])) raises an AttributeError while the query is being generated.

This PR expresses a list of values in the generated KG query by repeating the top-level property once per value, each copy being required and carrying a single value:

{"propertyName": "Qdevelopers1", "path": ".../developer", "required": true,
 "structure": [{"propertyName": "Qfamily_name", "path": ".../familyName",
                "filter": {"op": "CONTAINS", "value": "Baggins"}, "required": true}]},
{"propertyName": "Qdevelopers2", "path": ".../developer", "required": true,
 "structure": [{"propertyName": "Qfamily_name", "path": ".../familyName",
                "filter": {"op": "CONTAINS", "value": "Oakenshield"}, "required": true}]}

A result must therefore match every value in the list, in any order.

• A one-item list is treated as a single value, so the query is unchanged.
• An empty list raises a ValueError, as does more than one list within the same top-level property (e.g. lists for both developers__family_name and developers__given_name), since there is no way to pair the items.
• Other filters within the same property are repeated in each copy.
• A list of ID strings is accepted for a link property, as a single ID string already is.
• Equals and Regex values in a list keep their own operator.

The PR also fixes expand_filter(), which currently drops all but the last of several filters sharing a prefix, e.g. developers__given_name and developers__family_name (separate commit).

This is a first step towards supporting list-valued properties in existence queries: _build_existence_query() currently raises CannotBuildExistenceQuery("not implemented yet") for them, so objects such as a File with hashes are always treated as new when saved.

Tests

• Offline tests of the generated queries in test/test_queries.py, and of expand_filter() in test/test_utility.py.
• A live test, test_execute_query_with_list_filter, checks against the KG that filtering software versions on a list of two developer family names returns exactly the overlap between the two single-name queries. Previously, this test would have failed, producing a 500 error from the KG.