The mysterious death of Manhattan swimwear designer Martha Nolan-O’Slatarra at the upscale Montauk Yacht Club is being eyed as a possible accidental overdose, sources said Tuesday. The 33-year-old Irish beauty was found unconscious at the ritzy club around midnight Aug. 5 aboard a boat named Ripple — one of at least two Grateful Dead-themed crafts owned by insurance mogul Christopher […]