text: Title: [ENH] Friendlier error when neo4j creds not provided
  Body: Community user usability report: If Neo4j creds or a driver are not provided, the error currently looks like:
  
  ```
  /path/to/conda_env/lib/python3.8/site-packages/graphistry/plotter.py in cypher(self, query, params)
     1504         res = copy.copy(self)
     1505         driver = self._bolt_driver or PyGraphistry._config['bolt_driver']
  -> 1506         with driver.session() as session:
     1507             bolt_statement = session.run(query, **params)
     1508             graph = bolt_statement.graph()
  AttributeError: 'NoneType' object has no attribute 'session'
  ```
  
  It'd be more friendly to do something like:
  
  
  ```
  if driver is None:
      raise ValueError('No bolt  driver configured. Use register(bolt=...) to specify credentials or a driver.')
  ```