refactoring qad widgets part 1

c++ cast, nullptr, forward declaration, agregate ui, connect to member functions, order and clear includes

libs/widgets/qcodeedit.h

@@ -49,7 +49,7 @@ class QAD_WIDGETS_EXPORT QCodeEdit: public QWidget
 	friend class _QCE_Viewport;
 	
 public:
-	QCodeEdit(QWidget * parent = 0);
+	QCodeEdit(QWidget * parent = nullptr);
 	~QCodeEdit();
 	
 	enum ACClassType {
@@ -177,7 +177,7 @@ private:
 	bool hasBlockSelection() const;
 	void startBlockSelection();
 	void cancelBlockSelection();
-	void switchBlockSelection(QKeyEvent * ke = 0);
+	void switchBlockSelection(QKeyEvent * ke = nullptr);
 	bool removeBlockSelection(bool is_del);
 	void insertBlockSelection(QString text);
 	void createBlockSelection();