Bugs with Inset workflow

[will-moore]

• When I copy and paste panels with insets, we assign new inset IDs so that the new panel + inset are still linked via new IDs.
  However, if I do another copy and paste of the same panel + inset, I don't want these new panels to have the same new IDs as the others.

• If I copy and paste an Inset panel (e.g. to make split-view panels of the inset) but then I delete one of them, the Inset ROI gets removed from the parent image, even though we still have an Inset panel 'linked' to it.