make main layout available for subclassing

src/richtexteditordialog.cpp

@@ -2,7 +2,6 @@
 #include "htmltextedit.h"
 #include "htmlhighlighter.h"
 
-#include <QVBoxLayout>
 #include <QToolBar>
 #include <QDialogButtonBox>
 #include <QPushButton>
@@ -12,6 +11,7 @@ RichTextEditorDialog::RichTextEditorDialog(QWidget *parent)  :
     m_editor(new RichTextEditor()),
     m_text_edit(new HtmlTextEdit),
     m_tab_widget(new QTabWidget),
+    m_main_layout(new QVBoxLayout(this)),
     m_state(Clean),
     m_initialTab(RichTextIndex)
 {
@@ -54,9 +54,8 @@ RichTextEditorDialog::RichTextEditorDialog(QWidget *parent)  :
     connect(buttonBox, &QDialogButtonBox::accepted, this, &QDialog::accept);
     connect(buttonBox, &QDialogButtonBox::rejected, this, &QDialog::reject);
 
-    QVBoxLayout *layout = new QVBoxLayout(this);
-    layout->addWidget(m_tab_widget);
-    layout->addWidget(buttonBox);
+    m_main_layout->addWidget(m_tab_widget);
+    m_main_layout->addWidget(buttonBox);
 }
 
 RichTextEditorDialog::~RichTextEditorDialog()