OO-3404: allow to copy alien assessment item, show an error if the user try to copy an unreadable assessment item

OO-3396: make the QTI 1.2 results export resilient to missing result XML of a particular participant

OO-3386: calculate the relative path from the directory to the item to render correctly images in Word document

OO-3373: removing the indent of assessment item and test to prevent visual changes in the HTML rendered by browsers