added polymorphic calls

* Call targets are computed based on static types (same as variable action's dynamic types).
* Usage and definition finders now deal with accumulating information in the same variable action ('-arg-in-' or '-scope-in-'). That variable action is created in the VariableVisitor, and the transference is prepared at the end of the finder, instead of with each handleActualAction.
* ObjectTree: pattern now accepts any variable, including fake patterns like ('-root-' or '-arg-in-')
* Tests updated