* No longer use erroneous heuristics that depends on the assumption that
  for some model viewst there is a hidden root element (e.g., CA)
* Instead, use the model element handler service to determine object
  to be edited (same as object to be layouted).

Issue-Ref: 3433
Issue-Url: https://af3-developer.fortiss.org/issues/3433


Signed-off-by: Simon Barner <barner@fortiss.org>