Bug 20156: Display a markup for the current language in header menu

Bug 20156: Display a markup for the current language in header menu

This patch replaces Glyphicon markup with Font Awesome markup so that a
check mark appears next to the currently-selected language in the staff
client header's language menu.

Also changed in this patch: Some classes have been removed because they
are not used in staff client CSS.

To test you must have multiple languages installed and enabled in the
staff client.

 - Set the StaffLangSelectorMode system preference to "top" or "both top
   and footer"
 - Confirm that the currently-select language in the langauge menu has a
   check mark next to it.

Signed-off-by: Jon Knight <J.P.Knight@lboro.ac.uk>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>