A0 widget

Added the Auth0 login plugin.

There were already a shortcode to show the auth0 login form.
Here is a screenshot of both (the new widget and the shortcode) https://cloudup.com/c9Ze-siQEBg

Is there any way that two login form can be shown?
If I add the widget and the shortcode only shows one of them
Link to the main wiki instead of `#dict` here