implemented also SetCurrentDirectory()
If File not exists, GetLastAccessTime, GetLastWriteTime and GetCreateTime should return default value of 1601-01-01 (from MSDN: If the file described in the path parameter does not exist, this method returns 12:00 midnight, January 1, 1601 A.D. (C.E.) Coordinated Universal Time (UTC).)
MockFile.Move can now throw exceptions (ArgumentNullException, IOException & FileNotFoundException)