Fix Mac Specific Issues with Editor Window

[IntegerLimit]

This PR fixes two issues with the editor window, both mac specific:

• Crash with Cleanroom due to look and feel problems, fixed through defaulting to cross platform look and feel if system default is not accessible
• Fixes shortcuts using ctrl instead of cmd on Mac
  • Needed to use explicit system check, as Toolkit.getDefaultToolkit().getMenuShortcutKeyMask() is not an API available in Java 8