If we introduce the new Archive and File menus, it makes sense to introduce different Extract actions as well.
The implementation is a little tricky, since I had to use a third Extract action for the toolbar. Basically we have:

1. The Extract action in the Archive menu, which always extract the whole archive (even if the user selected some file).
2. The Extract action in the File menu, which is only enabled if some file has been selected, and extracts only those files.
3. The Extract action in the toolbar, which is the very same Extract action that Ark currently provides: it allows to extract the whole archive, or only the selected files (if any).

The action on the toolbar also gets the current CTRL+E shortcut, in order to not change the current behavior. The new actions don't have a shortcut yet, I couldn't find reasonable ones. Suggestions are welcome :)