Project summary page after a reviewer leaves a project

[bwallace]

Currently if a reviewer screens a bunch of abstracts for a review, then leaves, the project summary page will subsequently act as though this person never existed (no note is made of the number of abstracts she screened). This is because we query the ReviewersProjects table. To fix this we will have to also query the Labels table to grab the set of reviewers that ever contributed to the project.