Adds cycle detection as requested in #21.
This is achieved through a new ObservableList implementation called VetoableListDecorator, which allows Parents to veto changes that would create a cycle in the node hierarchy. Additionally, Parent checks for invalid nodes, such as duplicates or null values.
Description
Adds cycle detection as requested in #21. This is achieved through a new
ObservableListimplementation calledVetoableListDecorator, which allowsParents to veto changes that would create a cycle in the node hierarchy. Additionally,Parentchecks for invalid nodes, such as duplicates ornullvalues.