Sling TV has only been live for two weeks — but Dish Network chairman Charlie Ergen said today that he has big plans for the attention-grabbing $20-a-month video streaming service. It’s “part of a strategy to take content to a more mobile basis and a more wireless basis” — which is the way “the next generation is going to watch television” — he said in a conference call today. Ergen has been amassing wireless spectrum to help make the satellite company — which he…