Reviewer based on team.yml data

This changes the static assignment of reviewers in a bunch of projects. Instead one can use data from the team.yml / Reviewer roulette. Currently only choosing by role (e.g. maintainer / reviewer) is possible.

Only available reviewers are chosen. If no reviewer is available, it will fall back to the full list of potential reviewers.

This migrates a few projects to this new way of choosing reviewers.

Closes #21 (closed)