/// <summary>
 /// Called, when user creates link via "link tool"
 /// </summary>
 public bool CanCreateLink(SlideView slide1, SlideView slide2)
 {
     bool exists = false;
     exists = slide1.GetAllLinks().Any(l => l.ToSlideView == slide2 | l.FromSlideView == slide2);
     return !exists;
 }