What would you do if Hitler moved in next door? Two years ago the Foyle Film Festival screened Michael Beach Nichols and Christopher K. Walker’s documentary Welcome to Leith, a harrowing, stranger-than-fiction tale of Neo-Nazis trying to take over a tiny North Dakota town. I used to think about it about once a month. Now I think about it every day. Leith, Grant County is three square miles in size. You can fit the whole population in one train carriage. Its mayor is also the school bus driver. In 2012 it gets a new resident: a quiet, scraggy-haired older man…