Do not display technical XEM spaces in the WebHome Dashboard

Right now there's only the following spaces hidden;

#set($blacklistedSpaces = ["Import", "Panels", "Scheduler", "Stats", "XAppClasses", "XAppSheets", "XAppTemplates", "XWiki"])

We need to add the technical spaces used in XEM. In the future we need the hidden space feature so that we don't draw dependencies in the core about space names.