Fixes MultipleSelectInterface

It doesn't derive from IdentityInterface anymore (caused node removal
in workflows).

Also applied improved dynamictraited interfaces checking in workflows.
Moved private members from class to instance
Merge branch 'enh/GraftWorkflow' into experimental
fixed error
Merge branch 'enh/GraftWorkflow' into experimental
Added return cid in GraftWorkflow.insert
Changed access to child ids in GraftWorkflow
Merge branch 'enh/GraftWorkflow' into experimental