OO-2491: apply patch to always show coach comments (S. Clemenz), fix missing title of the course elements and their headers, fix missing legends, remove the old CSV and only use the OpenXML variant

OO-2484: add option "sendpartial", collect invalid addresses, convert addresses to identities and show an error in contact form

OO-2457: manual correction option will only update the score automatically and not the passed/failed status, clarify where own the user course env. and make it consistent for check list, don't show comment if there is only an empty string

OO-2479: reduce overhead everywhere, optimized and simplified query to count the participants of a group, bypass reloading the group set of identities, bypass reloading the base group of business group...

OO-2478: show a message if a user want to jump to a "softly" deleted course, don't send reminder of deleted course, show "deleted" course before "Members only"

OO-2442: implement an upgrader to set the status to inProgress for some old task course element entries, set the status if someone take a task or upload a file

OO-2472	: reactivate the user session cache for WebDAV to mitigate DOS like attack, set the session time out for REST and WebDAV session to 5 minutes

OO-2464: send publish after publishing is finished, speed up batch update of check lists and efficency statements...

OO-2462: make the due date mandatory if the due date enabled (slightly modified patch of S. Clemenz)