- updated to py2neo 1.6

__init__.py
- added global _cypherQuery() for direct Cypher queries
- SQLite database files are now temporary
- NodeFarm::addNode() only adds 'type' to a node if it's missing
- fixed Database::listNodeProperties() where clause
- re-added 'type' property to Relationships in Database::_addEdge()
- updated _getPy2neoMetadata