Implement an Owner / Privileged user system for special commands

[Vogel612]

It would be nice if "disruptive" commands like summon, unsummon and shutdown could only be executed by special people. These users should be maintained at runtime and persisted to the configuration, so as to be the same after restarts and the like.

[Unihedro]

Good idea. Timed ownership will be effective as well, especially during testing.