Snapping of graphical component doesn't work

[flandreas]

Pure graphical components like rectangles or circle don't perform component-to-component snapping, but just snap at the component's location. Instead, a rectangle should snap at its both sides and at the center, both horizontally and vertically. The reason for the bug is that graphical elements are wrapped by special wrapper when being added to a graph drawing, and this wrapper doesn't correctly forward snapping behavior to the wrapped graphical component.