This is just a play ground to fool around with the new mechanics of Vaadin v8.
This is not about beautiful code or best practises, but throwing everything at it, that's edgy, tricky, strange, ... in v7.
There only is one huge source file, with everything thrown in
/src/main/groovy/app/ui/AppUI.groovy
For project setup see https://github.com/christoph-frick/springboot-groovy-vaadin-starter