Show related objects on daemon worker task queue detail pages

Summary:
See PHI287. Currently, you can't get very much information about a task in the worker queue from the web UI.

This is largely intentional (e.g., it's bad if we let you inspect the content of a "send an administrator's password reset email" task), and a lot of the data is task-class specific so it would be a lot of work to expose it, but we can add one useful piece of information pretty easily: for tasks with an objectPHID that points at a valid object that's visible to the user, tell the user which object the task is associated with.

Test Plan:

Reviewers: amckinley

Reviewed By: amckinley

Differential Revision: https://secure.phabricator.com/D18890