* Compatibility with latest Neo4J 4.0.4

Starting with Neo4J v4, it no longer auto generates SSL/TLS
certificates if they aren't supplied. To keep the example
working, I needed config to specify whether the connection
to Neo4J should be encrypted or not.

It defaults to False, at the moment, so I think most
people would need to add an explicit True to their config.

* Satisfy warning and fix test failures.

The neo4j driver is now supposed to be imported using 'neo4j', the
older .v1 is now deprecated. I was going to leave this, but then
saw there are deprecation warnings.

Several unit tests were failing because they new 'neo4j_encrypted'
key wasn't included in the configs. I believe it makes sense to
include 'NEO4J_ENCRYPTED: True' as a default anyway. This should
stop people with existing configs from having to update them.

* Add a config parameter for SSL cert validation.