Have main page be a scoreboard page

```
@app.route("/")
def homepage():
return """
KarmaBot
"""
```

Instead of just returning the string `KarmaBot` when you hit https://slackkarmabot.herokuapp.com/, have it be a scoreboard of all the users' scores.

Start at the homepage route shown in the issue and inspect how the application stores or retrieves users' scores and whether it already has templates or related routes. Done means visiting / displays a scoreboard containing all users' scores instead of only the string "KarmaBot".

Written by the indexing model from the issue text.