Ensure timetableBackup is properly shutdown

[narendly]

b95f9e1#diff-c4c4d2dfc4872704464b23f5c7d876479444b2f393b60c4ebe5fb182b645cf00R196-R202

Here it synchronizes on the class reference, but this should synchronize on this for proper shutdown of the timetable backup thread. This is because notifyAll() is called on the object instance of TimetableBackup, not the static class reference itself.

-> UPDATE: (20MAY22), TimetableBackup.this is correct. The shutdown method is missing though (see below)

Also, BackupManager::stop() is missing timetableBackup.shutdown();