Unknown clients shouldn't be able to arm the alarm system

[Rowbotronics]

Accidentally deleted the client config for the front door, then the case fell open and hit the alarm button, arming the alarm. Couldn't disable it from the front because the client was unknown, so I tried the back, but the server wasn't responding. Loud noises happened, eventually restarted the server and got it disabled.

[domstoppable]

Code for the arming functionality should be moved to a plugin. This will prevent the server from processing newly-added clients (with no associated plugins) if they send arm messages.