CI/CD: GitHub Actions

[mkoskim]

Take GitHub actions in use. Goals:

1. Automated tests for commits whenever we have some
2. Build releases

Automated testing: One thing I am always paranoid is file saving (and other file system operations). Once upon a time I had small bug in my editor (either Python moe or Python mawe). It meant that it happily wrote empty files when saving. You can understand my feelings when I realized I had practically deleted the stories I edited...

So, there should not be errors in file saving! None. Nada. In case of emergency, the software should crash long before it starts writing invalid trees to files.

Release builds: It would be absolutely great, if GitHub would build Linux, Windows and Mac images when releasing. Basically we need just the latest release build, if anyone wants older versions, they can fetch the sources and build one by themselves.

Resources: Some quick googling about this:

https://github.com/marketplace/actions/electron-builder-action

https://stackoverflow.com/questions/76210268/error-when-building-my-electron-app-in-github-actions