Joindin 441: Redirecting the I'm attending button

Would someone be able to review my changes to Controller/Event.php, I'm not convinced that the way I'm doing the redirecting is the best way. If anyone can suggest something better that would be great.

Your import of the jquery library here might cause collisions in the `app/templates/Event/map.html.twig` view (don't know if it is used); you might want to remove the jquery.min.js include in that view