updated slide JavaScript to detect types better
The original method for detecting images is improved.  Now it looks for certain extensions at the end of the path part of the URL instead of at the end of the whole URL (with a query string on the URL there's a difference)
If it can't detect the content type based on the file extension, it will do a GET on the new Utilities/GetContentType route, sending the URL.  If everything fails, then it defaults to rendering the slide as a webpage.