use `graphviz` for graph drawing

As discussed in BAMWelDX/weldx#714 I think it would be worth giving the `networkx` + `(py)graphviz` option another chance

especially for more complex or stylized graphs this could lead to easier (and more flexible) solutions

example for TD
https://stackoverflow.com/a/39662097/11242411

ref:
http://www.graphviz.org/doc/info/attrs.html