utility: added FilePath abstraction and rewrote data management to use it

The utility class FilePath wraps an instance of boost::filesystem::path. Using FilePath allows for easy comparision of
file paths on different platforms using absolute or relative paths. Whereever file paths are compared, this wrapper
should be used.

src/lib/data/location/TokenLocation.h

@@ -5,6 +5,7 @@
 #include <ostream>
 #include <string>
 
+#include "utility/file/FilePath.h"
 #include "utility/types.h"
 
 class Token;
@@ -36,7 +37,7 @@ public:
 
 	unsigned int getColumnNumber() const;
 	unsigned int getLineNumber() const;
-	const std::string& getFilePath() const;
+	const FilePath& getFilePath() const;
 
 	TokenLocation* getOtherTokenLocation() const;
 	void setOtherTokenLocation(TokenLocation* location);