multiple chromosome display in QtSLiM #1287

Job	Run time
canceller	2s
tests-Windows-CLI (mingw64, x86_64, 3.8)	16m 27s
tests-Windows-CLI (ucrt64, ucrt-x86_64, 3.8)	16m 36s
tests-Unix-GUI (ubuntu-20.04, 5.9.5, 7)	4m 44s
tests-Unix-GUI (ubuntu-20.04, 5.15.2, 11)	5m 56s
tests-Unix-CLI (ubuntu-20.04, 7, 3.8)	6m 9s
tests-Unix-GUI (ubuntu-22.04, 5.15.2, 12)	6m 7s
tests-Windows-GUI (mingw64, x86_64)	12m 47s
tests-Unix-CLI (ubuntu-20.04, 11, 3.9)	6m 3s
tests-Unix-GUI (ubuntu-22.04, 6.7.2, 12)	6m 46s
tests-Windows-GUI (ucrt64, ucrt-x86_64)	12m 51s
tests-Unix-CLI (macos-12, 3.8)	11m 11s
tests-Unix-GUI (macos-12, 5.9.5)	6m 13s
tests-Unix-CLI (macos-13, 3.9)	8m 33s
tests-Unix-GUI (macos-13, 5.15.2)	6m 44s
tests-windows-latest-pacman (mingw64, x86_64)	1m 57s
tests-Unix-GUI (macos-13, 6.7.2)	8m 38s
tests-windows-latest-pacman (ucrt64, ucrt-x86_64)	1m 56s
	2h 19m 40s

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