Distinguish pieces in superposition

[LucjanJanowski]

Right now if I make left and right castle in superposition I have four castles on the board. CL1 (Castle Left in position 1), CL2 (Castle Left in position 2), CR1 (Castle Right in position 1), CR2 (...). By moving CL1 to a position when a measurement is made I influence the measurements of CL2 but probably not CR1 or CR2. Therefore, I think it should be marked somehow.

[caphindsight]

Sorry – it is unlikely that I will have time to work on this anytime soon. But happy to review a pull request if you want to make the change.