Start a proper test suite

[jmbowman]

PortaBase has managed surprisingly well all these years without an actual test suite, but it's long past time to start one. Decide on the framework to use and write the first few tests in it.

[jmbowman]

I'll probably try Qt Test for this; Squish also looks good, but it's commercial with no advertised pricing, and I don't want to deal with the licensing ramifications. Although I'd love to get this in place to sanity check the 2.3 release, it's honestly been far too long since the last release, so I'll just release what I have so far as 2.3 and see if I can get some basic testing in place when I finish the Qt 6 port.

[jmbowman]

This is one option for setting up an Android testing environment in GitHub Actions: https://medium.com/innovies-club/run-android-emulator-out-of-the-box-with-github-actions-b84cba766e62 .