R1:304c6a45976d

Improve UI and documentation for "Ignore Attributes" in Owners slightly

Summary:
See PHI251. Ref T13137.

- Replace the perplexing text box with a checkbox that explains what it does.
- Mention this feature in the documentation.

Test Plan:
- Clicked/unclicked checkbox.
- Read documentation.
- Used an existing checkbox control in Slowvote to make sure I didn't break it.

Reviewers: amckinley

Reviewed By: amckinley

Maniphest Tasks: T13137

Differential Revision: https://secure.phabricator.