AF networks: readability

[MennaRempt]

This issue is for both the Overlap network and the Transmission network.

• The relative proportions of the nodes and the labels have to be reevaluated. It’s better in the transmission network than in the overlap network (because of the varying node sizes?), but the labels are relatively large for the smaller nodes. This makes it difficult to read and interpret the network and to see to which node a label belongs. The readability of the labels has priority over the aesthetics of the visualisation.
• Moving nodes around: cf. Issue #579. It should be possible to move nodes around and have them remain where they are placed (or minimally jump back).

[shariboodts]

Only execute for Overlap network