Bump project to java versions past Java 8

[NeoCortex97]

I only have java 11, 14, and 17 instances on my system.
I tried launching the prebuilt jar, but I got countless errors regarding things that got removed from the java core with java 9 or later.
I tried opening the project in an IDE and fixed some problems with these things rather crudely.
I'm not that good with java, but I would assist you in updating the project to a current Java version.
And maybe a current spring version (I'm using spring at work, so I could help with that).

And as it seems, you are using some libraries (mainly junit) that you provide as a jar in your classpath and that don't show up in the maven project. Please fix that!!!
Either by specifying them as provided, or by simply as a normal dependency.

Otherwise the project seems really exciting and I'm looking forward to using it!

[NeoCortex97]

I looked further into your code and discovered something I didn't understand.
It may have to do with the spring boot version or something I don't understand.
I would advise to handle application startup differently. at least the GUI.
I would have the GUI start a separate Java process as a daemon process for the application instead of what you are doing.