OO-2790: add the options to upload assessment documents on a per course element / user base which behave like the user comment

OO-2742: reimplement start option (without autoplay), host in openolat flv.js and hls.js to prevent url with http/https blocked by Firefox, enhance useability of chapter editor

OO-2791: show an error message if a question of the pool is not readable during the import in a test

OO-2785: handle the checkbox property in home user search, coaching tool, import of user in group and course

OO-2785: special handling of generic checkbox because "not checked" is "I don't want to search with it"

OO-2732, OO-2784: add selenium test for the drag and drop variety of match interaction, update tests after OO-2784