ENH: Add a command prompt to the master server

[EliteMasterEric]

Ideally, running ./MasterServer should, aside from displaying logs, also provide a prompt with which commands can be run.

This terminal should have access to any commands a GM level 9 user would, and would allow running server operators to run commands without logging in.

[codeshaunted]

What would the commands be run from though? They need an entity to run on. A possibility could be a ghost GM9 player, or maybe even the zone control object.

[Xiphoseer]

For that to work without interrupting the game, you need separate threads and synchronization, which would great, but would also be a major change in how the game works right now. Much better might be something like #309 which is then called by another program.

_{(Trivia: This was a thing on LUNI way back when)}