RFE: move theme.txt from application folder on Mac

[IoTMike]

On the MacOS version, the Arduino UI "theme" file is stored inside the application container, e.g. Arduino/Java/lib/theme/theme.txt. Request that the contents of this file be moved outside of the application (so it withstands new application versions), say to the ~/Library/Arduino15/preferences.txt file or just move the theme.txt to ~/Library/Arduino15 folder. Thanks!

[per1234]

Fixed by #7115 (thanks Mumfrey!).