Add test suite for CypherService class
Add CypherService class
Adjust TDD test suites
use config file for Neo4j database host URL
Update GraphDatabase class
drop backwards compatibility for query method
Fix GraphDatabase class
create service instances in constructor to bind the right `this`
Move query method from GraphDatabase to CypherService class
Adjust CypherService class
retrieve service URL in separate method
Use extended exceptions for custom errors