“Arthur Christmas” is a spirited, comically chaotic and adorably anarchic addition to the world’s over-supply of holiday cartoons. It’s very British, in other words — from its producers (Aardman, the folks who gave us “Wallace & Gromit”) to its voice casting to the slang slung by the assorted Santas in this 3D computer-animated farce. “Assorted Santas?” [...]