Stop including FileUtils.h in any header

This causes every piece of code which wants to use CFile or CDir to have to
include FileUtils.h. This causes quite some noise.

Signed-off-by: Uli Schlachter <psychon@znc.in>

modules/extra/email.cpp

@@ -9,6 +9,7 @@
  * Author: imaginos <imaginos@imaginos.net>
  */
 
+#include "FileUtils.h"
 #include "MD5.h"
 #include "User.h"
 #include "znc.h"