By Michael Holden and Lucy Marks LONDON (Reuters) – While millions watched the Platinum Jubilee festivities to thank Queen Elizabeth and reflect on her 70 years on the British throne, for the monarchy itself, the four-day celebrations have also very much been about looking to the future. From parades in London and a party outside Buckingham Palace to a Service of Thanksgiving, many in Britain have been paying affectionate tributes to a 96-year-old who has reigned longer than any of her predecessors in 1,000 years. But the queen’s absence at many of the Jubilee events because of health issues m…