Oops, one renaming was missing...
waitinglist is now read from activities even in UI (step 2b)
Now we check against the activity waitinglist whether somebody is eligible to subscribe (step 3).
Now the UI sets the registration time period in the activity waitinglist. Finally, we could get rid of the waitinglistStore. (step 4)
Oops, we should rather save the activity... (step 4b)