Add Enabled Administrator UI setting

[jonpas]

Turns on or off the Administrator UI in the briefing diary. Useful for users with custom AAR frameworks in their missions/mods, persistence systems etc.

Admin UI will remain if setting is disabled during the mission, this could be handled but would require the setting to be in recorder component or an event being registered to handle the setting change in that component. As this is an admin tool, I consider it less important, but can be done if needed.

Alternative implementation would be to handle ocap_administratorList = "" (empty string indicating disabled), but this implementation is more clear and straightforward.