refactoring qad widgets part 2

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

libs/widgets/mathmatrixedit.cpp

@@ -1,6 +1,7 @@
 #include "mathmatrixedit.h"
-#include "qvariantedit_custom.h"
 #include "matrixedit.h"
+#include "qvariantedit_custom.h"
+#include "qad_types.h"
 #include <QBoxLayout>
 
 
@@ -43,7 +44,7 @@ void MathMatrixEdit::setReadOnly(bool yes) {
 class MathMatrixEditFactory: public QVariantEditorFactoryBase {
 public:
 	MathMatrixEditFactory() {}
-	virtual QWidget * createEditor() {return new MathMatrixEdit();}
+	QWidget * createEditor() override {return new MathMatrixEdit();}
 };