Add user warning on startup

notify the user of the use of dev software

ToDo: the text still needs to be adjusted

sources/main.cpp

@@ -22,6 +22,9 @@
 #include "machine_info.h"
 #include <QStyleFactory>
 
+#include <QtCore>
+#include <QtWidgets>
+
 /**
 	@brief myMessageOutput
 	for debugging
@@ -204,6 +207,32 @@ int main(int argc, char **argv)
 		delete my_ma;
 	}
 
+	if(! QET::FileFormatStable){
+		QMessageBox::StandardButton btn = QMessageBox::critical(
+			nullptr,
+			QCoreApplication::translate(
+				"main",
+				"Unstable file format!"),
+			QCoreApplication::translate(
+				"main",
+				"<p><b>ATTENTION: This application version is UNSTABLE!</b></p>"
+
+				"<p>Everything you do with this application can break your "
+				"workspace, libraries or projects! Saved files will not be "
+				"readable with stable releases of QElectroTech. It's highly "
+				"recommended to create a backup before proceeding. If you are "
+				"unsure, please download an official stable release instead.</p>"
+
+//				"<p>For details, please take a look at QElectroTech's "
+//				"<a href=\"%1\">versioning concept</a>.</p>"
+
+				"<p>Are you really sure to continue with the risk of breaking your "
+				"files?!</p>","this text is not finished yet, expect changes!")
+					.arg("doc_release_workflow"),
+					QMessageBox::Yes | QMessageBox::Cancel, QMessageBox::Cancel);
+		if (!(btn == QMessageBox::Yes))
+			return 1;
+	}
 	return app.exec();
 }