When she blew up in 2012, Lana Del Rey was an untouchable, unknowable character whose preoccupations with heartbreak, America and old stuff cast her as a tragic Hollywood icon in the mould of, say, Marilyn Monroe. But slowly, she’s opened up and let people in, and now, with brand new sixth album ‘Norman Fucking Rockwell’ raising eyebrows and blowing minds, she talks to Rhian Daly about America's failings, forest fires, Donald Trump – and reasons to be cheerful.