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-2454 Improve performance of video management: replace metadata xml with database adapt track files

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