One user per booking / booking locks
Idea It is required to have a possibility to make sure, that only one user is able to do modifications in one booking at the same time. Currently it is possible that multiple users do modifications on same booking at the same time, even if changes them self are only done once (first user).
Other users will get errors that rebooking is only valid on last sequence. Entered changes are deleted while displaying booking again.
Idea is to implement locking functionality on booking level. User has to check out/lock booking before any modification will be possible.
1. new flag in system settings `Buchungsänderungen nur nach Sperren der Buchung´ ( 
Flag will activate locking functionality. As default setting is off.
2. Implementation of new transaction code New action code 'DE' (Darstellung exklusiv/Display exclusive) is available for display bookings with locking functionality.
...