macOS 12 startup + fix multiuser GUI crash + misc cleanup

gradint-build/INSTALL.txt

gradint-build/Makefile

gradint-build/mac/install.sh

...-build/mac/start-gradint.app/Contents/MacOS/start-gradint

gradint-build/samples/utils/filemove.sh

gradint-build/samples/utils/trace.py

gradint-build/server/email-lesson-archive.sh

gradint-build/server/email-lesson-report.sh

gradint-build/server/email-lesson.sh

gradint-build/server/samples.cgi

gradint-build/src/booktime.py

gradint-build/src/filescan.py

gradint-build/src/frontend.py

gradint-build/src/lessonplan.py

gradint-build/src/loop.py

gradint-build/src/makeevent.py

gradint-build/src/play.py

gradint-build/src/recording.py

gradint-build/src/sequence.py

gradint-build/src/synth.py