LONDON (Reuters) – Pop music loves him. The art establishment shuns him. At the age of 80, British artist Peter Blake is revered for his celebrated "Sgt. Pepper" Beatles album cover yet at the same time dismissed as too "cheerful" to be one of the greats. Regularly stroking his wispy silver beard, and supported around a central London gallery by a walking cane, the man dubbed the "godfather of Pop art" still struggles to come to terms with his place in the world of contemporary culture. …