Remove last editor window after saving its properties

[facchinm]

Only OSX needs the "app" to stay open after handleQuit and to remove the editor windows when called.

Fixes #8337

[ArduinoBot]

✅ Build completed.

Please test this code using one of the following:

⬇️ http://downloads.arduino.cc/javaide/pull_requests/arduino-PR-8349-BUILD-817-linux32.tar.xz
⬇️ http://downloads.arduino.cc/javaide/pull_requests/arduino-PR-8349-BUILD-817-linux64.tar.xz
⬇️ http://downloads.arduino.cc/javaide/pull_requests/arduino-PR-8349-BUILD-817-windows.zip
⬇️ http://downloads.arduino.cc/javaide/pull_requests/arduino-PR-8349-BUILD-817-macosx.zip
⬇️ http://downloads.arduino.cc/javaide/pull_requests/arduino-PR-8349-BUILD-817-linuxarm.tar.xz

ℹ️ The linuxarm build is still experimental and may not be always available.

[vimes666]

Thanks for the swift response!
I tested http://downloads.arduino.cc/javaide/pull_requests/arduino-PR-8349-BUILD-817-linux64.tar.xz just now and the problem seems to be solved :)
As for windows, I dont know, my latest working version is 98. Someone else will have to test that.