Summary:
- See D2945.
- Drop `cache` field from ManiphestTransaction.
- Render task descriptions and transactions through PhabricatorMarkupEngine.
- Also pull the list of macros more lazily.
Test Plan:
- Verified transactions and transaction preview work correctly and interact with cache correctly.
- Verified tasks descriptions and task preview work correctly.
- Verified we don't hit the imagemacro table when we're rendering everything from cache anymore.
Reviewers: btrahan
Reviewed By: btrahan
CC: aran
Differential Revision: https://secure.phabricator.com/D2946
