Graph view enhancements

Currently only immediately connected nodes are shown in the graph view.

It would be super-nice to have a couple of other views:

- Show all predecessor nodes from the current node (including the source system)

- Show all successor nodes from the current node (including the target system)

This would make it a lot easier to understand the data flows.

Customizing the Graph view by expanding and collapsing nodes/connections would also be a very useful addition.