Allow disabling Gravatar

Resolves #3600

SoObjects/SOGo/SOGoDomainDefaults.m

@@ -1,6 +1,6 @@
 /* SOGoDomainDefaults.m - this file is part of SOGo
  *
- * Copyright (C) 2009-2015 Inverse inc.
+ * Copyright (C) 2009-2016 Inverse inc.
  *
  * This file is free software; you can redistribute it and/or modify
  * it under the terms of the GNU General Public License as published by
@@ -191,6 +191,11 @@
   return [self boolForKey: @"SOGoForceIMAPLoginWithEmail"];
 }
 
+- (BOOL) externalAvatarsEnabled
+{
+  return [self boolForKey: @"SOGoExternalAvatarsEnabled"];
+}
+
 - (BOOL) sieveScriptsEnabled
 {
   return [self boolForKey: @"SOGoSieveScriptsEnabled"];