Rigelian on Mac

With macOS Catalina Apple has released catalyst, which makes it possible to port an iPad app to a Mac app with limited effort. A few months ago I had a first look at this, but ran into too many problems. Yesterday I tried again with the latest versions of all frameworks, and was able to get a version running on my Macbook in less than 4 hours. The main issue I ran into is how to make existing subscriptions work on Mac as well.