Allow filtering Differential overviews by other participants

Summary:
This is useful for writing feedback - what did I work on with someone?
This creates AND IN (...) and not AND AND AND if more participants are specified.
User may not expect it but whatever, it works the same for the most common case of 1 extra participant.
It would be nice to have this also for other filters but it would by way harder.

Test Plan: Displayed my revisions with some specific reviewer and some elses revisions with me as reviewer.

Reviewers: epriestley

Reviewed By: epriestley

CC: wez, aran, Korvin

Differential Revision: https://secure.phabricator.com/D4408