To its 200 million-plus active users, Twitter is many things: a social network, a short-form messaging service, a news wire, a tool for self-expression — even, some believe, a force for global political change. But the company itself seems far more keen to position itself among its users — and even better, potential users – as a TV companion, an indispensable tool to keep up with, discuss and even influence the outcomes of shows and live events like sporting contests and political debates.