Impl better support for cypher queries and mapping return result to Neo4j::Node and Neo4j::Relationship objects, closes #68, closes #66, closes #65

* Cleaned up code and removed internal use of neo4j-cypher DSL
* Replaced Neo4j::Label.query with Neo4j::Session.query
* Made Neo4j::Session.query same as Neo4j..Session.current.query
* Added match, limit, skip, where, conditions, map_return, map_return_procs as query parameters, see YARD docs.