allow session options via 'config.neo4j.session_options'

All options from HTTParty are available. For more Information see http://rdoc.info/github/jnunemaker/httparty/HTTParty/ClassMethods

example:

config.neo4j.session_options = { basic_auth: { username: 'foo', password:  'bar'} }
config.neo4j.session_type = :server_db
config.neo4j.session_path = 'http://localhost:7474'