Add missing header to KoPageWidgetItem.h

same as KoDocumentInfoDlg.h, from which this class declaration was extracted

libs/main/KoPageWidgetItem.h

+/* This file is part of the KDE project
+   Copyright (c) 2000 Simon Hausmann <hausmann@kde.org>
+                 2006 Martin Pfeiffer <hubipete@gmx.net>
+
+   This library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Library General Public
+   License as published by the Free Software Foundation; either
+   version 2 of the License, or (at your option) any later version.
+
+   This library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Library General Public License for more details.
+
+   You should have received a copy of the GNU Library General Public License
+   along with this library; see the file COPYING.LIB.  If not, write to
+   the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
+   Boston, MA 02110-1301, USA.
+*/
+
 #ifndef KOPAGEWIDGETITEM_H
 #define KOPAGEWIDGETITEM_H
 
-#include <kpagewidgetmodel.h>
 #include "komain_export.h"
 
+class QWidget;
+class QString;
+
 // This class can be implemented when we want to extend the
 // dialog with new, specific pages.
 class KOMAIN_EXPORT KoPageWidgetItem
 {
-
 public:
-
     virtual ~KoPageWidgetItem() {}
+
     virtual QWidget *widget() = 0;
     virtual QString name() const = 0;
     virtual QString iconName() const = 0;