New App: Chess.com ELO Tracker

This adds a new app: A chess.com ELO tracker. With this app, a user
can track the their current ELO across several game types and time
controls.

Options are as follows:

- Username: a Chess.com username
- Stat1: A game type to track (tidbyt#1)
- Stat2: A game type to track (tidbyt#2)
- Stat3: A game type to track (tidbyt#3)
- Show Change: Shows how far you've grown or fallen from the past 30
days.