logic: used wstring in FilePath constructor

* used wstring in FilePath constructor where easily possible
* added FilePath concatenate method that accepts string parameter
* implemented using only wstring in MessageStatus
* used wstring in config

src/lib_gui/qt/QtApplication.cpp

@@ -26,7 +26,7 @@ bool QtApplication::event(QEvent *event)
 	{
 		QFileOpenEvent* fileEvent = dynamic_cast<QFileOpenEvent*>(event);
 
-		FilePath path(fileEvent->file().toStdString());
+		FilePath path(fileEvent->file().toStdWString());
 
 		if (path.exists() && (path.extension() == ".srctrlprj" || path.extension() == ".coatiproject"))
 		{