migrate snode->isnode
fix SNode
fix SModel
fix SNode.getModel
SModel.xxxRoot - arg type fix
fix SModel iterables as ret types
fix SNodeAccessUtil
fix refs collection copying
fix SNodeAccessUtil
migrate SNode.getReferences
migrate SNode.getChildren
SNode: constructors
SNode: constructors: just-constructed nodes have old SNode type
fix SNodeAccessUtil
fix getChildren: ret value
fixing type problems
add casts to SNode where needed (not all)
instantiaeConcept() returns old SNode
add casts to SNode where needed (not all)
dealing with SNode.getChildren ret type