OO-1593: allow to add images in QTI editors and enhance rendering of medias with relative path between manifest / test / items

OO-1919: try to find more informations for a good warning message if group/areas are renamed and / or deleted in enrollment course element

OO-1926: added formaDateRelative to formatter to add a specific period of time to a baseline date and format it short. made it available in the phantomJS certificates