J. Joseph Ricketts, the wealthy executive who considered and then dropped a proposal to revive controversy over the relationship between President Obama and his former pastor, is a rising conservative maverick with ties to the Chicago Cubs team. He’s also linked to a super political action committee that bankrolled an upset in Nebraska’s recent Republican Senate primary. A politically conservative Nebraskan known as “Joe,’’ Ricketts built the TD Ameritrade brokerage firm into a billion-dollar empire that backed the purchase of the Cubs as well as interests in film, media, resorts and bison meat products.