title: No webapp folder in output jar
body: <p>I'm building a simple web application using Vaadin and Spring Boot. When I build it using <code>mvn package</code> and run via <code>java -jar &lt;path_to_jar&gt;</code> it seems to work.</p>
  
  <p>But one thing puzzles me. When I'm inside the project folder and run <code>java -jar target/app.jar</code> it seems to be working properly. But if I go outside and run it as <code>java -jar &lt;full_path_to_jar&gt;</code> it works, but the theme is gone. I checked the output of Chrome Inspector and it returns <code>404</code> for <code>/VAADIN/themes/mytheme/styles.css?v=7.5.5</code></p>
  
  <p>How do I package the theme into the jar?</p>