Mutiny Mode Fixes

* Updates the fluff text to use 'Nyx' instead of 'Tau Ceti'.
* On the 'Check Antagonists' panel, admins can view the remaining Directive X objectives and can reassign the Head Loyalist and Head Mutineer.
* Refactors the admin panel code into a new code file, mutiny_admin.dm, for separation.
* Adds loyalists and mutineers to ghost AntagHUD.
* Player Mobs that don't have minds won't be picked as candidates for Directive X.