Add historical stats information to website

[DesiPilla]

The functionality to pull historical stats about a league already exists in doritostats.fetch_utils.py - get_historical_stats(). There are then analysis functions such as weekly_stats_analysis() and season_stats_analysis() that can provide interesting insights based on this data, as well as an infinite number of ad-hoc analyses.

I suggest adding the ability to download a team's historical data to the website.
I also suggest showing the output of weekly_stats_analysis() and season_stats_analysis() in templates/league.html.