PARIS (Reuters) - European car registrations fell 3.6 percent in March, the main regional industry group said on Wednesday, with Nissan and Ford showing some of the biggest sales declines.Registrations in the EU and European Free Trade Association (EFTA) countries dropped to 1.77 million cars last month from 1.84 million a year earlier, the Brussels-based Association of European Carmakers said.The auto industry is facing a downturn in European demand just as it struggles to make drastic cuts to..