The phrase ‘dark comedy’ recurs in descriptions of the filmography of Martin McDonagh, the London-born but Irish-descended playwright turned film-maker who this week received a Golden Globe for his third feature, Three Billboards Outside Ebbing, Missouri. It’s the kind of loose, generous generic signifier that covers a multitude of structural and tonal sins. Sin is something McDonagh seems very interested in, populating his films with ugly people hopscotching across ugly situations. Redemption is a tricky prospect, both for the characters and for McDonagh himself, who lumbers Three Billboards with much the same problems that made In Bruges and Seven Psychopaths such…