[script|dmenu] Add option to make row permanent.

fixes: #1952

include/modes/dmenuscriptshared.h

@@ -26,6 +26,9 @@ typedef struct {
   /** non-selectable */
   gboolean nonselectable;
 
+  /** permanent */
+  gboolean permanent;
+
   /** urgent */
   gboolean urgent;
   /** active */