Add get Releeph Requests conduit method

Summary: Added "getrequests" conduit method

Test Plan: Open /conduit/method/differential.getrequests/ and try different inputs.

Reviewers: edward, epriestley

Reviewed By: edward

CC: aran, epriestley, Korvin

Maniphest Tasks: T3057

Differential Revision: https://secure.phabricator.com/D5788