Parenting

handle EC_Placeable parentRefs so that if a parentRef is set when the component data is received (from server now, later can come from file too) we delay the creation of the view (now three.js scene node) until the parent has been created .. so can attach the child to it correctly right away.

works, but is far from perfect yet, issues:

- does not support a hierarchy of multiple levels of parents

- does not handle later parentRef changes (view assumes the ready signal from EC_Placeable is the first one)