Add win probability API and graphs

[andschneider]

This adds a win probability endpoint from the stats API and graphs in the Schedule and Gameday views.

• In the Schedule tab, the whole game win probability is shown so you can get a quick overview of the flow of the game. This is heavily inspired by Baseball Savant's win probability graph.

• In the Gameday tab, the last few at bats are shown with more stats around the win probability for that specific at bat. The at bat selection scrolls with the plays, which lets you see how impactful specific at bats were to the win probability. The info is:
  • leverage index (li)
  • win probability added (wpa)
  • home team win probability (win)