UI class

Sample UI class src/groovy/app/MyUI.groovy which contains code that just shows a label in the web browser.

We can immediatelly start coding Vaadin application using that file, or maybe rather do a refactoring. For example, rename the file to AppUI.groovy and move it to different package (folder) src/groovy/com/company/app. Then you need to change mapping property inside VaadinConfig.groovy.