R1:da1ebac8d8fa

Allow Nuance items to provide curtain panels, link to imported tasks, parse comments

Summary:
Ref T10537.

- Let nuance items render custom curtain panels.
- Add a custom panel linking to the imported task, if one exists.
- Actually extract comments properly.

Test Plan:
Unit tests, plus:

{F1193800}

{F1193801}

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10537

Differential Revision: https://secure.phabricator.com/D15537