Add ablility to include alias and category on register

Right now when you have push-config.json in order to add alias and categories you'll have to load it yourself and then add those properties. It would be nicer if one could just append them in the register like so:

$fh.push(onNotification, successHandler, errorHandler, {alias: "me@me.com", categories: ["sport", "news"]}); //alias and categories will be merged with existing config