Distinguish Pull Request authorship from review contributions

[eternoendless]

There is no silver bullet to precisely assess the "value" of any given contribution. In comparison to commits, I think Pull Request authorship provides the "less bad" way to count contributions.

Alternatively, we could have a drop-down allowing you to choose between:

• Pull requests – only the author counts here
• Reviews – all review events on the project as tracked by Github's API (example)