PARIS (Reuters) – Sales growth in the global luxury market will slow this year to 5 percent from 13 percent in 2011 at constant exchange rates as Chinese customers rein in their spending and concerns about the global economy take their toll, a study has found. A closely watched report published on Monday by consultancy Bain & Co together with Italian luxury goods trade body Altagamma said the first signs of a deceleration began to appear in 2012 in China, the luxury industry’s main engine of growth. …