Improve keynav
Improve keynav

Using gtk_widget_keynav_failed() instead of hardcoding
gtk_widget_error_bell() gives applications a chance to override
keynav handling. We will make use of this in the power panel
to 'link' arrow keynav across multiple list boxes.

https://bugzilla.gnome.org/show_bug.cgi?id=692275

GNOME/egg-list-box,GNOME/egg-list-box,GNOME/egg-list-box