Partially modernize Doorkeeper/Asana bridge

Summary: Fixes T6201. This stuff didn't fully get updated for ApplicationTransactions. Get it working again (notably, make inline comment text publish) and clean it up a little bit.

Test Plan:
  - Published a Differential feed story into Asana with comment text.
  - Pulbished a Diffusion feed story into Asana with comment text.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T6201

Differential Revision: https://secure.phabricator.com/D10584