add methods to get the base cdn - one protected that returns the cdn uri or null if cdn stuff isn't set up, and one public which is helpful for page code that uses the cdn if available and falls back to the site if unavailable (ala SiteImage)
add methods to get the base cdn - one protected that returns the cdn uri or null if cdn stuff isn't set up, and one public which is helpful for page code that uses the cdn if available and falls back to the site if unavailable (ala SiteImage)


svn commit r58857

silverorange/site,silverorange/site,nburka/site,nburka/site