Describe the bug

When you disable the first stage of a multi-stage rocket, the CG & CP is still referenced to the front of the sustainer stage, whereas it should be to the front of the "new first stage".

It would probably also be best to update the rulers, since those are also still referenced to the sustainer.

To Reproduce

Disable first stage of multi-staged rocket

Screenshots / .ork file

Screenshot(s):

OpenRocket version

22.02, unstable

What platform are you running on?

macOS

Additional context

I guess this is a bit of a personal preference, so I'll ask @hcraigmiller, @neilweinstock & @JoePfeiffer for their opinion on this.