Release 3.9

[prmr]

• Make sure all other issues for the milestone are closed;
• Clean up any small code problem
• Generate a fresh user guide using the tip generator
• Run all the unit tests;
• Increment the version number in JetUML.java;
• Update the copyrights using the copyright tool;
• Update the documentation;
• Check/Update the build config
• Merge to main branch
• Create a new release;
• Write the release notes;
• Release the application on GitHub;
• Create a thin jar that only includes the source code (excluding tests) and the license;
• Package the application as above for the three different platforms, and upload to the release
• Compute SHA values and sign the binaries
• Close the milestone;
• Delete stale branches