Updates /Playing page

Because I really like making Manuel suffer, I updated the /playing page too. I copied over most of what I built for the /reading page to keep the two pages consistent. Filling this "database" will be a bit trickier, though, especially for games that aren't played through Steam. For Steam games, I hook into the Steam API, so most of the backend data is populated automatically. Everything else I have to enter by hand. Even so, it's still a big improvement over the previous version, where everything had to be entered manually. The data will really become useful going forward. I have a script running every night that pulls the deltas since the previous sync to update playtime, streaks, and other statistics automatically.