Motivation for this change

Quoting James Ahlstrom, http://james.ahlstrom.name/quisk/CHANGELOG.txt :

Quisk Version 4.1.73 November 2020

I rewrote the logic for SoftRock I/Q amplitude and phase corrections. The new logic will enable much better
image suppression because it can correct I/Q based on both the VFO and the tuning offset. If you do nothing,
there is no change in the corrections. To use the new logic, enter new correction data. Use the Help button
on the Config/radio/Config correction screens. Corrections are in the file quisk_init.json, and you should
make a copy of this file to save your current corrections.

I added a missing version.h file to SoapySDR. It is not clear that this fixes the version check for the
change in the Soapy API. Please test.

When using the Split button, Quisk now leaves the Rx frequency unchanged and splits the Tx frequency.

I added a new band "Aux1" that can be checked on the Config/radio/Bands screen. It can be used as a special
band for a panadapter or when Quisk is used as a 10.7 MHz IF.

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.