OO-2531: implement print and download raw dat for QTI 2.1 in statistics views, refine list of users seen by admin, authors, coaches in statistics (courses and resources) and in asessment tool

OO-2526: don't write the marker file anymore, make the buffer configurable, add some close session...

OO-2515: save the master file untouched, deliver  more pixels for the print view of the members course element, add REST api methods to check if a particular size of portrait is available