Relationship generation: allow no directionality

[slobentanzer]

For query generation, it may be useful to have undirected relationships at the query stage; i.e., a bidirectional relationship is represented by just one directed relationship in Cypher, but the query is executed without an angled bracket, -[]- instead of -[]->. This is recommended by Neo4j.

To implement, we would change the query generation to reflect this, iff either the source and target annotation in the schema config are missing, or the field undirected is set to true, explicitly.