Photo: Boston Renegades When you’ve played professional football for nearly two decades, there aren’t many things that can phase you. When the Renegades open another title defense on Saturday against the D.C. Divas, six-time champ and four-time MVP quarterback Allison Cahill will be as cool as a cucumber despite some new faces on the team and a much bigger target on the organization’s collective back. As we wrote in our…