logic: Return to last scroll position in code view on undo

* fixed scrolling on undo
* refactored autoscrolling in code view
* save scroll position of user with MessageScrollCode

src/lib_gui/qt/element/QtCodeArea.cpp

@@ -173,6 +173,11 @@ std::shared_ptr<TokenLocationFile> QtCodeArea::getTokenLocationFile() const
 	return m_locationFile;
 }
 
+QtCodeFile* QtCodeArea::getFile() const
+{
+	return m_fileWidget;
+}
+
 void QtCodeArea::lineNumberAreaPaintEvent(QPaintEvent *event)
 {
 	QPainter painter(m_lineNumberArea);