OGM-622 Upgrade Neo4j version to 2.1.5

https://hibernate.atlassian.net/browse/OGM-622

At the moment `org.neo4j:neo4j` includes different version of the same libraries. While this is not usually a problem because maven will automagically select only one to resolve conflicts this is a problme for because we use the enforce plugin.

That's the reason in the BOM I exclude some dependencies from neo4 to include them with the rgiht version.

I've talked with the Neo4j folks and they agreed to apply a patch if I send it, I will do that soon.
Ok, so I thought all the Neo4j artifacts would be available in the version 2.1.5. But apparently neo4j-cypher-compiler-1.9 and neo4j-cypher-compiler-2.0 are only available in 2.0.3/2.0.4. In that version they pull in transitive dependencies in different versions than Neo4j core 2.1.5, hence the error raised by the enforcer plug-in.

So actually the Neo4j folks should release a consistent set of their artifacts which all use the same versions of transitives.

That being said, I find the fix via the exlusions a bit confusing. I think the better way would be to declare the versions of all the concerned (transitive) dependencies in the BOM to match the version referenced by Neo4j core 2.1.5.