From “Who Shot J.R.?” to the infamous “Dream Season,” here’s the best and worst Ewing family moments on its 45th Anniversary — Dallas — the super-soap that defined the decade of the eighties — celebrates its 45th anniversary today. Spawning three made-for-TV movies, the long-running Knots Landing spin-off, and a 2012 TNT reboot, Dallas’ cultural impact is unmatched. Larry Hagman, who starred for fourteen seasons as Texas oil tycoon J.R. …