entered with Plater::enter_gizmos_stack(), and left with
Plater::enter_gizmos_stack(). Other than that, the 2nd Undo / Redo
stack is transparent to the user of the Plater.
WIP: Currently the Gizmo stack takes a snapshot of the whole scene on
Plater::enter_gizmos_stack(). While it should work, it may be cheaper
to modify the Undo/Redo stack to only take a snapshot of the gizmos
in the Gizmo mode.
The Snapshot specific data, which is fully provided from the outside
of the Undo / Redo stack is now stored as an StackData structure.
The StackData structure may be extended with small size data,
like the cursor position in the side bar.
remembering the last selected Printer profile for the SLA and FDM
technologies separately, and activating them on Undo / Redo.
When switching the technologies, user is asked whether to discard
the modified profiles or not.
starting from the objects of lowest ObjectID.
(convex hulls are recoverable as well as the indexed triangle sets
inside the TriangleMeshes or the triangle connectivity information).
Now the top most snapshot (the temp one taken before Undo jump) will
never be released.
