Add data information to daemon task view

Summary:
Load the data for daemon worker tasks when viewing them, and present
the information in a useful way. This defaults to printing the json data,
but for some classes of worker it will also link to the corresponding
object, to make debugging problems with workers easier.

Test Plan:
load /daemon/task/NNN for a CommitParserWorker and a MetaMTAWorker, and
see the addition of a data field with useful content and link.

Reviewers: epriestley, vrana

Reviewed By: epriestley

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D4226