Find all selected items at one level starting from the largest level. This is required to be able to modify multiple rows in the table editor. Items in the table editor use by default SelectionManager::FIRST_LEVEL
When using toggle buttons in tree view, the current field changed might be outside of the current selection. Only apply multiple field changed if current field is part of the current selection.
Move Add and Delete command features there.
Implement generic Toggle Commands.
Make library an cmake "OBJECT" library to allow "registering by static initialization".
Add the concept of CurrentContextMenuTargetWidget into CmdFeatureManager to support the toggle commands.
Updated test application to use the new commands
