Unable to remove math node

[Bowen Li]

Removing a visual component in a page cannot remove its corresponding math node.
using lp:~libowen96/workcraft/trunk-son-refactoring
- create some places in Petri net plug-in
- combine them into a page
- enter the page and remove one place
- use Tool -> Test tool -> Math level test to output all math places
The removed node still exist.

[Danil Sokolov (danilovesky)]

The methods inRef and decRef in DefaultMathNodeRemover that were based on a reference counting are changed to track the sets of dependant nodes:

private void addReference(MathNode mathNode, DependentNode dependentNode) {
  if (mathNode != null) {
   HashSet<DependentNode> refs = referenceTracker.get(mathNode);
   if (refs == null) {
    refs = new HashSet<DependentNode>();
    referenceTracker.put(mathNode ,refs);
   }
   refs.add(dependentNode);
  }
 }

 private void removeReference(MathNode mathNode, DependentNode dependentNode) {
  if (mathNode != null) {
   HashSet<DependentNode> refs = referenceTracker.get(mathNode);
   if (refs != null) {
    refs.remove(dependentNode);
   }
   if ((refs == null) || refs.isEmpty()) {
    referenceTracker.remove(mathNode);
    Node parent = mathNode.getParent();
    if (parent instanceof Container) {
     ((Container)parent).remove(mathNode);
    }
   }
  }
 }