A Democratic power broker in southern New Jersey was accused Monday of leading a 12-year racketeering scheme to influence local economic development plans, buy up waterfront property and reap millions of dollars in tax credits. The allegations against George Norcross, 68, include threatening a developer who refused to sell the property rights needed for Norcross and his five codefendants to build the tallest building on the Camden waterfront. Norcross told the developer he would “f— you up like you’ve never been f—– up before,” according to a 13-count, 111-page indictment quietly filed la…