fix inbox#581 Caps Lock inverts shortcuts
Testing summary:
- Improves situation on all platforms, no regressions
- Not fixed: On Windows, "Caps Lock" really behaves like "Shift Lock", non-letter keys with a Shift variant are still affected by Caps Lock. E.g. "CapsLock+6" still behaves like "Shift+6". But letter keys like "Ctrl+S" and "Ctrl+Shift+S" now work independent of Caps Lock state.
- Not fixed: Setting new shortcuts in "Preferences > Interface > Keyboard Shortcuts". This is still affected by Caps Lock on all platforms.
Edited by Thomas Holder