authenticate user within mongo facet helpers
authenticate user within mongo facet helpers

If authentication settings are provided then the user will be
authenticated for the MongoDB connection.

closes #93

nbargnesi/openbel-server,OpenBEL/openbel-api,OpenBEL/openbel-server,OpenBEL/openbel-server,OpenBEL/openbel-api,OpenBEL/openbel-api,nbargnesi/openbel-server,OpenBEL/openbel-server,nbargnesi/openbel-server,OpenBEL/openbel-api