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/settings/ApplicationSettings.h

@@ -89,7 +89,7 @@ public:
 	bool getMultiProcessIndexingEnabled() const;
 	void setMultiProcessIndexingEnabled(bool enabled);
 
-	std::string getJavaPath() const;
+	FilePath getJavaPath() const;
 	void setJavaPath(const FilePath& path);
 
 	int getJavaMaximumMemory() const;