CHICAGO — Hundreds of protesters blocked store entrances and shut down four lanes of traffic in Chicago’s ritziest shopping district on Black Friday to draw attention to the 2014 police killing of a black teenager who was shot 16 times by a white officer. Demonstrators shrugged off a cold drizzling rain to turn the traditional start of the holiday shopping season on Michigan Avenue’s Magnificent Mile into a high-profile platform from which to deliver their message: The killing of 17-year-old Laquan McDonald was another example of what they say is the systemic disregard police show for the lives and rights of black people. They chanted “16 shots!