Remove Neo4J OGM

[oxisto]

We want to get rid of the Neo4J OGM (and its annotations) since it burdens us that we need to design our node in a certain way that we are not happy with. Because we still want to support neo4j as a persistence and visualisation target, the first step was a new persistence layer that directly invokes CYPHER commands without the need for neo4j-ogm.

This issue serves as a collection of things remaining to do before we can remove the neo4j-ogm completely