web: update window title depending on active module

Fixes #4982

UI/MailerUI/UIxMailMainFrame.m

@@ -1,5 +1,5 @@
 /*
-  Copyright (C) 2007-2014 Inverse inc.
+  Copyright (C) 2007-2022 Inverse inc.
 
   This file is part of SOGo.
 
@@ -74,6 +74,11 @@
   [super dealloc];
 }
 
+- (NSString *) moduleName
+{
+  return [self commonLabelForKey: @"Mail"];
+}
+
 - (NSString *) modulePath
 {
   return @"Mail";