A six-story Upper East Side townhouse that cost its owner over $16 million to buy and renovate is now on the market for just under $9 million — a staggering $7 million loss. The seller, who requested anonymity, bought 238 1/2 E. 83rd St. in January 2013 for $2.6 million and spent $13.6 million tricking out the place — adding levels and installing custom-made marble floors, mahogany panels, an elevator, central air and a sophisticated security system. “He did it knowing full well he likely