Import fixups and change review commit semantics

This PR fixes some lingering issues and strengthens import review action validation.

It also separates the "update review action" and "commit review action" steps to allow for explicit review confirmation. This will help facilitate the "pull request" workflow where multiple people can work on a review without necessarily committing the review.

Future PRs may incorporate further PR review semantics (like reviewers adding comments on participants or participant attributes like phone numbers / email addresses).