By Martin Fricker The heartbroken parents of missing Madeleine McCann will tomorrow light a candle to mark her 21st birthday – just as they have for her past 17 birthdays. Kate and Gerry McCann, unable to celebrate their beloved daughter’s milestone with her, will once again put gifts and cards in her bedroom. There will be no loud party, no handing over the keys to the door. What there will be instead is prayer and hope – hope that Madeleine is alive and that finally, after 17 years, they will be reunited with their daughter. Madeleine was nine days shy of her fourth birthday when she vanish…