Make long relations nicer without arcs

[jcklie]

Is your feature request related to a problem? Please describe. Relations spanning more than a row are sometimes not looking good, especially if there are many of these.

Describe the solution you'd like Several things are thinkable:

1. Use numbers at source and target
2. Use same color something around source and target, e.g. underline

Hide the arcs, on hover, highlight both as always