Chilling new details emerged Sunday in the plot to attack Big Apple synagogues, including how the mastermind told cops he runs an online white supremacist group and has Nazi memorabilia because “it is really cool,” court documents allege. Christopher Brown, 21, who tweeted anti-Semitic threats with the username VrillKhan and under the handle @VrillGod, told cops he and accused cohort Matthew Mahrer met at St. Patrick’s Cathedral in Manhattan on Friday to carry out the attacks before they were busted. Police said the pair had purchased a Glock 9mm handgun for $650 in Pennsylvania. “I have a sick personality,” Brown...