Add events per catalog

Event scheduler:

• All events are global (done)
• Allow users to add, enable and disable the events in their own catalog (done)
• If things goes wrong, only disable events for the current catalog
• startup_events(bool noacl_or_bootstrap) needs to be changed to read events from all catalogs with catalog->event_scheduler == EVENTS_ON
• Normal users should not be able to disable event scheduler.
• If catalog->event_scheduler == DISABLED then the user should not be able to add events.
• The call to events->start() in event_scheduler_update() should only enable events for the current catalog.
• The call to events->stop() in event_scheduler_update() should only disable events for the current catalog.
• catalog events should be stopped when the catalog is deleted