set default JavaFX preload URL

this is a follow up to enable:

6735003: preload deployment common cache (plugin/webstart) with javafx libraries

When the above fix was integrated, JavaFX team did not have the URL set for the preload yet. Now they have it ready and documented at:

http://csgweb.sfbay.sun.com/wiki/bin/view/Main/JavaFXURLs

So we should set default preload url to: http://dl.javafx.com/javafx-cache.jnlp