Installation of Vaadin 8 in Eclipse

I just had a 2-day fight with Eclipse trying to get a Vaadin 8 IDE up and running. Finally it worked, even though the Vaadin documentation was sadly lacking. Here is my report:
https://stackoverflow.com/questions/48930717/install-vaadin8-in-eclipse
. Some of the information might be useful to enhance the Vaadin documentation.

If someone let me know how to do it myself, I offer to do it.