Enable figures of nodes, port, and labels to cover edges.

[sailingKieler]

In some projects there's the need for node figures to cover edges, i.e. to be drawn on top of edges.
This can already be achieved globally via the EDGES_FIRST configuration property

KLighD/plugins/de.cau.cs.kieler.klighd/src/de/cau/cs/kieler/klighd/util/KlighdProperties.java

Lines 308 to 313 in 59ea61f

	/**
	* Property for globally determining whether edges should be drawn before nodes, leading to
	* the effect of overpainting edges by nodes with background color.
	*/
	public static final IProperty<Boolean> EDGES_FIRST = new Property<Boolean>(
	"klighd.edgesFirst", false);

This issue demands for a more fine-grained solution allowing to configure this property per KGraphElement or even KRendering.

Current options:

• Classic approach (default): Edges are drawn on top of nodes (some with oversized highlighting figures)
  
• Alternative setup: Edges are drawn first, nodes are drawn second on top of the edges;
  this does not work for diagrams with edges crossing hierarchy boundaries
  Problem: oversized highlighting figures cover edges
  
• Requested setup: A parent node's children can be independently tagged to be drawn underneath or on top of the edges