NEW HAVEN >> The mobile "boot" - size 747 - was the dead giveaway.L.L. Bean's bootmobile backed into place on the traffic island off Broadway Monday to signal the next business Yale University will add to its concentration of shopping options in this part of the city.The two-level, 9,000-square-foot store is scheduled to open in summer 2018 as the larger retail component of the graduate student housing under construction at 272 Elm St.