ocarina: Set playlist tab label justify

I like the centered look better.

Signed-off-by: Bryan Schumaker <bjschuma@gmail.com>

ocarina/playlist/playlist.cpp

@@ -35,6 +35,7 @@ namespace ocarina
 		label = gtk_label_new("");
 		box   = gtk_vbox_new(FALSE, 0);
 
+		gtk_label_set_justify(GTK_LABEL(label), GTK_JUSTIFY_CENTER);
 		setup_treeview();
 
 		gtk_widget_show(label);