ISIS-537 Fix JavaScript for org.apache.isis.viewer.wicket.ui.components.widgets.cssmenu.AjaxDeferredBehaviour.OpenUrlStrategy#NEW_WINDOW. It should be wrapped in a function.

https://trello.com/c/UYl51kIt/101-todoitem-opensourcecodeongithub-a-no-arg-action-returning-a-java-net-url-does-nothing