[Feature request] Add existing plots to a new Scene

[asinghvi17]

Continuing discussion from Slack,

From Simon:

in theory it's easy to add the plots of one scene to another... the only problem is, how to interpret it?
do you just completely overlay them? do you inherit new defaults / the camera / the axis?
would it be just like plot!(parent, child.plots) ?
the last one would be easy to implement^^

My thinking is that we don't auto - update!, but do pass on the camera and axis from the parent Scene - essentially replotting the data with the kwargs might be one way to make it work, and we'd have it decomposed into a plottable (or even atomic) form.

[asinghvi17]

This is kind of like PlotSpec/PlotList now, but the idea was that the observables also commute. Will have to test if that's still the case.