Mike Segar/ReutersRoyalist is The Daily Beast’s newsletter for all things royal and Royal Family. Subscribe here to get it in your inbox every Sunday.Prince Harry and Meghan Markle went head to head with Prince William and Kate Middleton Tuesday, as the warring couples associated themselves with mental health campaigns and initiatives on both sides of the Atlantic on World Mental Health Day.Harry and Meghan were in New York, where they were the stars of a glossy mental health conference at Hudso