Further generalise Swissmon EPR regions

[qpavsmi]

Description

The EPR partition regions used in the Swissmon example are quite not optimal and general enough to cover all parameter sets:

1. The gaps around each arm of the central cross can be varied so to cover this option we would need 4 different regions for the cross instead of the current 1 region named cross.
2. The couplers now have 3 different regions, but they will always have the same gaps defined by b. Either we can collect all of the couplers in the same region or change Swissmon implementation to allow different gaps for each coupler to make use of the existing regions. If all of the couplers are put into the same region they can be collected in the default / complement region to simplify the code
3. Add a wire region around the junction
4. Optional: Make the couplers grounded somehow. This is currently not possible as the cross-section needs to contain a signal layer

[AbdullahKazi500]

I would be interested to work on this later on when I have some time to commit looks like a good issue