Implemented class code checking using chrome tab title

This branch uses the current active tab title in order to check what class we are leaving a review for so the user doesn't have to put it in manually. It also checks to see if the current active tab is one belonging to a valid myplan class page, and prevents the form from submitting if the user currently isn't on a myplan class page. It also informs the user of what class they are leaving a review for if they are on a valid class page.