Fix bug with editing operator with child data
Fix bug with editing operator with child data

This fixes a bug where if we started editing a manual manipulation operator
that has already produced output, the spacing that gets set on the parent
would be propagated down to the child.

To avoid this, mark the child units as modified so that the propagation does
not occur.

Signed-off-by: Patrick Avery <743342299f279e7a8c3ff5eb40671fce3e95f13a@kitware.com>

OpenChemistry/tomviz,OpenChemistry/tomviz,OpenChemistry/tomviz,OpenChemistry/tomviz