By Ben Hirschler LONDON (Reuters) - GlaxoSmithKline, Britain's biggest drugmaker, is placing a small but important bet on a new way of treating diseases by targeting electrical signals in the body. The company said on Wednesday it would offer a $1 million prize to stimulate innovation in the field, as well as funding up to 40 researchers working in external laboratories. The initiative is a long-term gamble on the promise of a new kind of medicine, using electrical impulses rather than the chemicals or biological molecules found in today's drugs. ...