deskutils/ganttproject: Update to 2.8.10

• Assign to myself
• Clean up port
• Make start script executable again (broken in r478989)
• Do not install Windows/macOS files
• Do not install license file twice
• Update Java version to minimum recommended version

Changes: https://github.com/bardsoftware/ganttproject/releases/tag/ganttproject-2.8.10