Add 'dependsOn' array to ConduitApi_maniphest_Method::buildTaskInfoDictionaries() return

Summary: Adds the PHIDs of the tasks that the current task depends on.

Test Plan: Use conduit to query a task with and without tasks it depends on.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D5892