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/element/QtLocationPicker.cpp

@@ -99,7 +99,7 @@ void QtLocationPicker::changeEvent(QEvent *event)
 
 void QtLocationPicker::handleButtonPress()
 {
-	FilePath path(m_data->text().toStdString());
+	FilePath path(m_data->text().toStdWString());
 	if (!path.empty() && !path.isAbsolute() && !m_relativeRootDirectory.empty())
 	{
 		path = m_relativeRootDirectory.getConcatenated(path);