Add the ability for Rooms to have a URL.

The URL is shown on the schedule and the event/proposal page.
The URL is only when a user is logged in and registered.

app/controllers/admin/rooms_controller.rb

@@ -48,7 +48,7 @@ module Admin
     private
 
     def room_params
-      params.require(:room).permit(:name, :size)
+      params.require(:room).permit(:name, :size, :url)
     end
   end
 end