Resolve "Anpassung der Pfeildarstellung"

All types of connection between two nodes are visually implemented, that are one way, self or both way connection. The label of the Predicate are the qname of the predicate uri or when multiple connections are taking the same direction, the number of predicates.

These label text size and visibility are bound to the user "zoom scale". If the user zooms in or out of the viewport, then an variable will be adjusted to this behavior. If the user zooms out of the viewport enough, the text on the arrows (the label of the predicate) and inside the nodes (uri,value or qname) will be turned invisible. But the user zooms back in these texts will be visible again and depending on the intensity scaled down.

Closes #12 (closed)