make main layout available for subclassing

include/richtexteditordialog.h

@@ -6,6 +6,7 @@
 #include <QDialog>
 #include <QTextEdit>
 #include <QTabWidget>
+#include <QVBoxLayout>
 
 class RichTextEditorDialog : public QDialog
 {
@@ -30,6 +31,7 @@ private:
     RichTextEditor *m_editor;
     QTextEdit      *m_text_edit;
     QTabWidget     *m_tab_widget;
+    QVBoxLayout    *m_main_layout;
     State m_state;
     int m_initialTab;
 };