Add Session-ID to header

add the room key to the header on every lecturer view to ensure that even late participants can join.

added UX label

assigned to @lmas60

added ToDo label

changed the description

changed milestone to %EDULEARN19

added WIP label and removed ToDo label

added ready for review label and removed WIP label

mentioned in merge request !240 (merged)

mentioned in commit c7d2ece6

closed via merge request !240 (merged)