code: public boolean removeCellLink(GridCell<P> cell) {
  		final int idx = this.cells.indexOf(cell);
  		if (idx >= 0) {
  			this.cells.remove(idx);
  		}
  		return idx == 0;
  	}
docs: Add a reference from this element to a cell that is containing this element.
  
  @param cell the grid cell.
  @return <code>true</code> if the removed cell is the reference;
  <code>false</code> if the removed cell is not the reference.