#3218 / download.php / export

Implemented spinning wheel (hourglass) displayed during rendering and downloading PDF.
Link.php, Report.php: New $vars[NAME_EXTRA_CONTENT_WRAP] which holds a '<button>' definition with necesary 'data-*' attributes. The Modal Dialog needs a uniq html id (derived from ttContentUid). That one is returned to Report() if there is at least one download element.