Maintenance command line for external programs

It would be very nice if external programs supported a maintenance command-line so all the configuration for a door could be in one place in scfg.

While this could be as simple as referencing a timed event, it would be awesome if there was an optional dependency between running the door and the maintenance event... basically, only run maint when no nodes are in the door, and don't allow a user to enter the door when the maint even is running on any node.