Don't include FileUtils.h in znc.h or Modules.h

Both these headers only really need CFile* which can be handled with a forward
declaration.

To make this possible, some methods are moved from the header file into the
corresponding implementation file, because they used CFile or CDir static
members.

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

HTTPSock.cpp

@@ -6,8 +6,9 @@
  * by the Free Software Foundation.
  */
 
-#include "Modules.h"
 #include "HTTPSock.h"
+#include "FileUtils.h"
+#include "Modules.h"
 #include "znc.h"
 
 #include <sstream>