Represent subnetworks in network-area diagrams

[So-Fras]

Describe the current behavior

A network can be composed of several subnetworks that have been merged together. Those subnetworks are linked through tie lines.
When drawing a network-area diagram of a network composed of 2 subnetwroks, there is no way to tell which subnetwork a voltage level belongs to.

Describe the expected behavior

The subnetworks should be easily distinguishable from one another.

Several ideas could be tested jointly or separately:

• Represent tie lines differently from lines (by adding an element at the center of the tie lines for example, see wath is already done in SvgWriter > drawEdgeCenter)
• Draw each subnetwork separately (when using a force layout) in order to have 2 "clouds of points" on each side of the image, with the tie lines in between.
• Elements of each subnetwork could be highlighted with a different color:
  

Describe the motivation

This feature would allow users to be able to make subnetworks out at a glance

Extra Information

No response