“Wildlife” is just plain wonderful, and I’ll explain the plain part in a minute. This coming-of-age drama is the directorial debut of the actor Paul Dano; he and Zoe Kazan adapted the screenplay from the novel by Richard Ford. The time is 1960, the place is Montana and the hero, a lonely 14-year-old named Joe Brinson, is trying to understand the ways of the world through his suddenly fractured family.