The Las Vegas Raiders will have a QB competition to determine their Week 1 starter. Kirk Cousins is the likely favorite, given that he knows the offense new head coach Klint Kubiak is trying to install, which would allow No. 1 pick Fernando Mendoza to learn. Nonetheless, it is an open competition, and if Cousins gets complacent or doesn’t take it seriously, it could allow for Mendoza to win the starting job. Moreover, there’s also the possibilit…