Introduce bindable properties for bounds

I propose to introduce width and height properties for Node object that are binded to getLayoutBounds().getWidth() and getHeight() respectively.

I'm asking this for the following reason: currently it is not possible to bind to Node's width and height. Actually you need to obtain layout bounds object and the get its width and height instead of just straitforward binding to two properties.

Those properties could look like this:

DoubleBinding() {

  { bind(layoutBoundsProperty(); }

  @Override public double computeValue() {
    return getLayoutBounds().getWidth();
  }

}