Connect Graphviz nodes directly instead of using strings

[Clifford-appliedAI-GmbH]

Currently there a lot of

s1, s2 = "abc", "xzy"
node1, node2 = pydot.Node(s1, ...), pydot.Node(s2, ...)
edge = pydot.Edge(s1, s2)

This is fine for smaller bits of code, but it can be a bit unclear when the code is more complex since we're connecting the nodes by "coincidentally" giving relevant things the same string names. It might be a bit better to move towards

edge = pydot.Edge(node1.get_name(), node2.get_name())