Keyboard shortcut for Preferences dialog

[RedBearAK]

Please add a keyboard shortcut binding to open the Preferences dialog.

It has become somewhat common on GNOME apps to use Ctrl+comma for opening preferences, so that is what I will suggest as the shortcut. This echoes the Cmd+comma that works in most macOS apps, and the Shift+Ctrl+comma that is used in a number of KDE apps that I've used.

I use a keymapper config that mimics the keyboard behavior of macOS in Linux desktop environments, so I could potentially remap my "Cmd+comma" shortcut to anything for this application, but there has to be some kind of keybinding in place to map onto. If the shortcut was Ctrl+comma it would "just work", like in other GTK apps I use, such as Text Editor.