function loadPage(pageName, pageHolder, useLoadingScreen, callback, isSubPage)
{
    pageHolder = pageHolder == undefined || pageHolder == null ? "#pageHolder" : pageHolder;
    useLoadingScreen = useLoadingScreen == undefined || useLoadingScreen == null ? true : useLoadingScreen;
    isSubPage = isSubPage == undefined ||  isSubPage == null ? false : isSubPage;
}