Sec/medical HUD users now receive relevant broadcasts

Users of security HUDs now receive broadcast messages from security bots. Similarly, users of medical HUDs receive broadcast messages from medical bots.
These messages can be enabled/disabled for individual bots through their standard configuration menu.

![Freeze, scumbag](https://www.dropbox.com/s/perfsp2lfo58u64/BotBroadcast.png?dl=1)

Also fixes a runtime error detected during development.
Basically having one proc which defines ````set [some category] = [...]```` calling another proc defining exactly the same category causes an infinite loop which is force-terminated. Calling it enough times then makes the server force-stop itself.

This proc was originally inherited by ai/robot.dm which complemented it using ````set category = "AI/Robot Command````. Only this gave drones access to the verb and I didn't want that. Realize now I could probably just explicitly remove it in their new() proc instead, for better code.