Use more modern code

[cristan]

The current code is based of grails 2 and the project is created by Groovy/Grails Tools Suite. Especially the latter is an issue because this hasn't been maintained in years and the official download link is now dead.

Grails 3 would be a great option since it's build on top off Spring Boot, so IDE support should probably be fine. You could even get it to work with Kotlin although the main advantage of this route would mostly be that you don't need to rewrite that much of the code.

Another option is to skip Grails altogether, and just make a Kotlin Spring (boot) project. You'll miss out on the nice features to persist items in the database, so you'll have to manually do the hibernate work (or use some other method to persist data).