Mayor Rahm Emanuel invoked the spirit of Daniel Burnham Thursday, unveiling a $1 billion plan to transform the way business travelers and tourists get from O’Hare International Airport to the Loop by allowing Tesla’s Elon Musk’s The Boring Co. to dig a high-speed speed tunnel across the Northwest Side, which the mayor referred to as “the X” — like a next generation version of the L we all know and tolerate.