Root node mechanism for GlobalReferences changed

Each global reference may have root node defined, by adding a node ID
(name or class) followed by root path separator “://“, e.g.:

@MyRootNode://SomeOtherNodeName/@OtherNode

First, MyRootNode will be searched recursively, starting from the
referencing node’s parent node and going up to. When found, relative to
it a Node named SomeOtherNodeName will be searched in root’s children
and if found OtherNode in its children.