By Michael Holden and Kate Holton LONDON (Reuters) -Horse-loving Queen Elizabeth was thanked for being “in the saddle” for 70 years as head of state at a service on Friday to celebrate her Platinum Jubilee, an event she missed due to her “mobility issues”. Other senior members of the royal family joined a congregation of politicians, charity figures and groups the queen has supported for the National Service of Thanksgiving at St Paul’s Cathedral in London to pay tribute to the sovereign’s record-breaking reign. Four days of celebrations began on Thursday when a beaming Elizabeth waved to crow…