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.
That's why we have tests, if you remove it you will have an exception at runtime since Neo4j check some of the classes included in this package.

I guess they are included in Neo4j since you can specify which compiler version you want to use. not sure why they are not optional. When I've asked them in the forum they said that they haven't thought about it.

Anyway, This is just one of the transitive dependencies included with Neo4j. I'm not sure why you have so many problems with it :)