PATCH for Chrome QTI Download

Fix for the exporting problems with a QTI XML file in Chrome and should also help improve performance and efficiency in other browsers as well. Now it will just flat out download the XML document for you.

To reproduce the old problem:

Create a test/quiz in Samigo
Try to export it as QTI xml
In chrome when you try to save the page, it will only save the HTML of the page, not the actual XML document.

This fix just downloads the actual document without rendering any other HTML pages.

This is my first time contributing a patch so please let me know if anything else is needed.