Create installer / standalone executable

[HEdingfield]

Determine the workflow needed to create a platform-independent installer and/or standalone executable for each serious release.

[gngilbert]

This would be very good to have but I have no idea how much work is involved.

[HEdingfield]

Now that we use Gradle, we can look into using jpackage to create separate installers for each platform.

Some info here: https://openjdk.java.net/jeps/343
Also read this entire answer: https://stackoverflow.com/a/54065502/3846321

If we can do this, it will probably effectively fix #282 also.

[rrojas350]

Originally removed to make room for other issues but this request has popped back up. Updating as a lower priority item and a nice-to-have if possible.

[HEdingfield]

@artoonie was able to close this after years with #660! 🥳