WWJ LayerSet updated

I put here the link to the updated version.

Basically I have added a couple of useful methods to query if an object or a class is contained by the LayerSet or some other contained Layer.

    @Override
    public boolean contains(Object o) {

        if (super.contains(o)) {
            return true;
        }

        for (Iterator it = this.iterator(); it.hasNext();) {
            Layer layer = it.next();
            if (layer instanceof LayerList) {
                if (((LayerList) layer).contains(o)) {
                    return true;
                }
            }
        }

        return false;
    }

Finally, I have added the mothod 'indexOf' that given a class returns the first instance ocurrence in the list (the search is not recursively).