"Move groups" moves unwanted data

[westram]

status quo:

• move groups copies the whole container ("group node") from old to new
• this copies
  • wanted taxonomy-related group-data (name, keeled-state, folded-state, …) and
  • unwanted taxonomy-independent group-data (linewidth, angles, …)
• if target contains taxonomy-independent group-data
  • that data is overwritten (erased when source does not contain such data).
  • a wrong "overwrite" message is logged for each unnamed target-node.
• bootstrap values in target get erased (did not check cause)

wanted behavior:

• ignore taxonomy-independent data
• create group-nodes in target where missing, keep+modify where already present
• keep existing comments