Add alumni section to /credits

[stakats]

Under "Contributors" we should add "Alumni", where we can move names of people no longer working on the project.

[flachware]

I thought we would use 'Contributors' for all people ever worked on the project and 'Team' on the homepage for the current team?

[inukshuk]

Didn't we want to remove 'Team' from the homepage?

[stakats]

Having 'Team' on the homepage was definitely more important when there wasn't really anything else to show there. How about moving 'Team' to /credits, with 'Alumni' (or we can call it something else) under it?

[flachware]

Alright, but let’s wait until we have the new version of the homepage, otherwise it would look quite short.