fix(mail(js)): hide sign and encrypt options if not usable

When composing a message, don't offer to sign nor encrypt the message
if user has not uploaded a certificate or if S/MIME is disabled.

SoObjects/SOGo/SOGoUser.m

@@ -945,7 +945,7 @@
   [mailAccount setObject: delegates  forKey: @"delegates"];
 
   // 9. Security
-  if ([[_defaults mailCertificate] length])
+  if ([[self domainDefaults] mailCertificateEnabled] && [[_defaults mailCertificate] length])
     {
       security = [NSMutableDictionary new];