Transactions - introduce a buildTransactionTimeline function

Summary: ...way way down in PhabricatorController. Use it on ManiphestTaskDetailController to test it. Ref T4712. I think the pager logic to be added as part of T4712 can safely reside entirely within this method. As I said earlier, 5 parameters is a lot, so I don't really want to add more. Next diff would do the pagination logic and the diff after that would deploy it everywhere. If while deploying it everywhere I find something off, that will be a different diff.

Test Plan: viewed maniphest tasks and they looked as spiffy as ever.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T4712

Differential Revision: https://secure.phabricator.com/D10844