Parent / Child cleanup

Work to cleanup the way parent / child relationships work.

Previously children were always a member of the root scene, with this
change only entities with no parent are a member of the root scene.

More validation has been added to catch weird cases.

Still a work in progress.
UI layout tweak for layer editor
Fixed params copy bug

Params were not copied correctly when the message was cloned.
Added layer moving

Layer move forward / backward.