Feature: A controller that tracks other existing controllers, with a configurable time-delay.

[KnightofStJohn]

Basically, a new controller type, that can be set to track the value of any of the already existing controllers, but with a time delay which is configurable.

This would allow for effects in the plume to "follow" events, and propagate through the plume. for instance, you could make pressure variations in the plume to propagate through the length of the plume, by letting the shock cones expand each after the other, so that it looks like a pressure wave going along the length of the plume.