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
this is to upgrade from auth0-widget-5 to lock. Right now, it is tied to lock-6.min.js and will be updated until the next major release.

If we want to force the update, I added an internal version counter (other than the AUTH0_DB_VERSION) to manage the settings updates.