Add Neo4j Bolt-based connector

[agarciadom]

We had to develop the OrientDB driver to make it possible to redistribute Hawk under the EPL (leaving the Neo4j driver for users to compile manually). However, Gabor told me about a new Apache-licensed driver for Neo4j that connects to a Neo4j 3.0+ server through the Bolt protocol:

https://github.com/neo4j/neo4j-java-driver

I think it'd be nice if we tried this driver and compared its performance against embedded OrientDB.