Credits to

• Rob Camick: Relative Layout
  https://tips4java.wordpress.com/2008/11/02/relative-layout/
   
• Ernie Yu: Java Swing range slider
  https://ernienotes.wordpress.com/2010/12/27/creating-a-java-swing-range-slider/
   
• Alvin Alexander: Java: How to copy an image to the clipboard
  https://alvinalexander.com/java/java-copy-image-to-clipboard-example
   
• Mozilla Foundation: Font "Fira Sans Medium"
  https://github.com/mozilla/Fira
   

Thanks to

• the JAVA community, especially „stack overflow“
  http://stackoverflow.com/questions/tagged/java
   
• the authors of „Geany“
  http://geany.org