#23 Improve keyboard shortcut display

[Martin Herrmann]

In the main window, some actions have a function key shortcut in addition to their regular one. For example, "New flight" has both "Ctrl+N" and "F2".

Currently, the function key is displayed as part of the text, like "New flight (F2)". It would be better to right-align the function key, along with the regular shortcut, like "F2, Ctrl+N".

On Linux/GTK, we can use a tab character (\t) for right alignment. However, this removes the automatically added shortcut, which we would have to re-add.

1. is this portable, especially to Windows?
2. can the original shortcut be added in a way that's portable and (potentially) properly localized?