Cleaning up the JME github org

I also made some changes to the Contributors team permissions, this team no longer has direct push access and now has full triage access. The Contributors team was our largest group with push permissions, but in practice nobody pushes to master in jME. The established workflow has long been to open PRs and have a core member or release manager review and merge them. So the push access was effectively just unnecessary attack surface. With full triage access, contributors can help by labeling, managing, and closing issues, and contributions can continue through the usual PR workflow.