Talk about living in the Upside Down. It’s not often a celebrity airs their dirtiest laundry in public. But singer Lily Allen shocked everyone last Friday with her new album “West End Girl,” which appears to present everything you ever wanted to know — and much, much more — about why  her marriage to “Stranger Things” star David Harbour  went off the rails. “I found a shoebox full of handwritten letters from brokenhearted women,” she sings on “Pu–y Palace ,” a song about visiting a partner’s