NEW YORK — An obsessed Taylor Swift fan has been arrested for stalking and threatening the star, police said Saturday. Joshua Christian, 35, showed up to the “Blank Space” singer’s Franklin St. townhouse in Tribeca June 12 and began barking threats through an intercom, cops said. The Brooklyn man allegedly hit the intercom and threatened to “hurt her if they weren’t together,” a police source said. Swift was not home at the time and her security team notified police later that day, law enforcement sources said. Christian also allegedly waltzed through an unlocked front door of the home March 2…