added option to specify referer in options passed to authenticate function

I ran into problems calling a feature service query against a non-public feature service.  I have a feature service hosted on ArcGIS Online that is shared only with my organization. From a web application, if I use geoservices-js authenticate to get a token and then use the token in a call to geoservices-js featureservice.query, an invalid token error is thrown.  Removing the hard-coded referer parameter of "arcgis-node" and setting the referer parameter of the authenticate request to match the host of the web application fixed the problem.  So I think allowing a client to specify the referer is needed.