If it wasn’t already, it’s become very obvious that Mikel Arteta has completely changed the atmosphere at Arsenal during his time at the club. Perhaps Tuesday’s victory over FC Porto at the Emirates was the biggest testament to how far Arsenal have come under Arteta. Not only because they progressed to the quarter-finals of the Champions League, but also just how united the whole club appeared. The Arsenal fans played a huge part in the win, jeering so incredibly loudly during the penalty shootout, a deafening atmosphere for a Porto player to keep their head in. And the scenes after Arsenal pr…