Dialog to allow user to log in to third parties

Creates the ability to have a dialog pop up when a user wants to log in to a third party to interact: e.g. disqus, youtube, instapaper, etc.
Arguably instead of "do nothing", we should remember that the user picked this option until the page is reloaded.  Because one day, some script is going to keep retrying and we're going to keep firing our popup.