Add a Top Contributors Tab?

[ajbozarth]

@JoshRosen I've created a Top Contributors tab that lists the top 15 contributors for each component based on number of PRs authors and commented on. I've already added this feature to one of my personal branches (that includes other extra features like only showing a certain group's PRs) if you want to take a look: https://github.com/ajbozarth/spark-pr-dashboard/tree/stc Note that how I calculate and cache the lists is very hacky and is reason this isn't a PR. If this is something you think we want then I can branch out the changes and take input on a better way to store and update the data. I'll also attach some screenshots of it below: