refactoring qad widgets part 1

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

libs/widgets/qcodeedit.cpp

@@ -3,6 +3,7 @@
 #include <QLayout>
 #include <QBoxLayout>
 #include <QScrollBar>
+#include <QLineEdit>
 #include <QTextDocument>
 #include <QTextDocumentFragment>
 #include <QTextOption>
@@ -11,6 +12,7 @@
 #include <QAction>
 #include <QApplication>
 #include <QDesktopServices>
+#include <QPainter>
 #if QT_VERSION >= QT_VERSION_CHECK(5, 0, 0)
 #  include <QWindow>
 #endif
@@ -24,7 +26,7 @@ Q_DECLARE_METATYPE(QCodeEdit::ACEntry)
 
 class _QCE_Viewport: public QWidget {
 public:
-	_QCE_Viewport(QWidget * p = 0): QWidget(p) {
+	_QCE_Viewport(QWidget * p = nullptr): QWidget(p) {
 		setObjectName("__qcodeedit_viewport__");
 		setMouseTracking(true);
 		//setCursor(Qt::IBeamCursor);