Redesigned the Calculus page to be divided into Calculus 1 and Calculus 2 tabs. The Calculus page now has an overview of the sub-pages. This was separated to look nicer and prevent excessive scrolling to get to the Calculus 2 videos.

All pages from now on will be built like this. I will likely push Discrete Mathematics into a more general Mathematics tab alongside Calculus when more series of videos are complete.