Modularize "related objects" menu items in Maniphest

Summary:
Ref T11179. This generates the Maniphest menu items in a modular way. It doesn't change any of the underlying code yet.

Searching for commits doesn't work particularly well so I've just hidden that for now, but the item itself works fine.

Test Plan: {F1696849}

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T11179

Differential Revision: https://secure.phabricator.com/D16162