As a moderator I want to select all/none participants to speed up my work flow

• If there are more than 2 participants listed, Insert "All/None" checkbox as first checkbox
• If at least one participant is NOT checked, the "all/none" checkbox selects the remaining participants
• If all participants are selected the all/none checkbox deselects all participants
• All/none is always "deselected" if at one or more participant are deselected (consider manual changes by user)
• All/none is "selected" if all participants are selected (consider manual changes by user)
• The All/none checkbox shows only the text "Mark All" or "Mark None" fitting to state situation

• No E2E needed (this feature is UI luxury)
• Update user doc