assignments on the base schedule are shown in the pages for the
schedule, read-only.
This allows managing things like breaks and misc sessions separately
from the regular WG sessions.
Base schedules are not allowed to be the base of other base schedules
(the hierarchy can only be one level deep) to simplify the mental
model and the code.
Add link for creating new schedules instead of relying on copying
Empty-Schedule and change the meeting creation code to no longer
create the special Empty-Schedule. Instead a "base" schedule is
created and a first schedule with the name and permissions of the user
creating the meeting, using "base" as base.
Speed up a couple of the Secretariat/AD agenda views by adding
prefetches.
- Legacy-Id: 18355
