Pluralize the names of the abstract user groups.

Created by: kfogel

In the 2020-03-17 meeting, we decided on some abstract user groups ("OutsideReviewer", "DecisionMaker", etc) that would, in theory, be useful for lots of competitions. Unfortunately, we hadn't yet settled on our standard of using plurals for group names (so that the name of our test user for that group can be the singular form).

So some day it would be nice if those abstract group names all got pluralized ("OutsideReviewers", "DecisionMakers", etc). This will require some manual updating of users and groups in various wikis.