fix(mail): add default label & color for $forwarded flag

Fixes #5534

SoObjects/SOGo/SOGoDefaults.plist

@@ -139,6 +139,7 @@
         $label3 = ("Personal", "#009900");
         $label4 = ("To Do", "#3333FF");
         $label5 = ("Later", "#993399");
+        $forwarded = ("Forwarded", "#B01FE3");
         $mdnsent = ("Return Receipt Sent", "#006600");
     };