OO-2723: store the webfeed in the database instead of xml files to enhance the reliability of blogs and podcasts

OO-1620: add modifier informations if available, add publication and modification item if in the time frame of the notifications

OO-1620: mark as new podcast and blog, rewrite part of the notifications handlers, fix some issues reading the ids of the publishers

OO-2732 beautify d&d question type, use color coding and border styles to distinguish between source and target

OO-2784 optimize sections, add item id (hidden), compile offline files for download, beautify coach comment