Docker images and JDK 13

Tags: #<Tag:0x00007f4913855d50> #<Tag:0x00007f4913855c88> #<Tag:0x00007f4913855ad0> #<Tag:0x00007f4913855a08>

The platform Docker images are now all shipped with an OpenJDK 13.

Version 4.0 patch level P24 and more recent are now compiled with a JDK 13 (instead of JDK 12 previously) but still in JDK 1.8 compatibility mode. (Open)JDK 13 is thus now the preferred JDK version to run Simplicité.

By the way, we have simplified the Docker image tagging scheme and we have also added two images for legacy versions 3.1 and 3.2.