Export datetime in better parseable format (i.e. full years etc.)

By default mdb-export will export dates in a format like: "08/31/04 23:59:00". This is very unpractical, because we don't know whether the year should be 2004 or 1904. This modification exports the date in a format such as: '31-08-1904 23:59:00', which is directly parseable using DateTime.parse and includes the century correctly.