beamer template: added 'navigation' variable.

Valid values are empty (default), frame, vertical, horizontal.

default.beamer

@@ -20,6 +20,7 @@ $endif$
 \setbeamertemplate{caption}[numbered]
 \setbeamertemplate{caption label separator}{: }
 \setbeamercolor{caption name}{fg=normal text.fg}
+\beamertemplatenavigationsymbols$if(navigation)$$navigation$$else$empty$endif$
 $if(fontfamily)$
 \usepackage[$for(fontfamilyoptions)$$fontfamilyoptions$$sep$,$endfor$]{$fontfamily$}
 $else$