Reviewing pull requests on a per-commit basis (BB-15978)

When reviewing pull requests, there is an "Overview" tab that shows the full diff and allows adding comments to particular changed lines. Through out the review process multiple fixes can emerge and trying to keep our history clean we rewrite our PR commits. Luckily Bitbucket can handle that and outdated comments can be still found (and Activity tab is a life saver).
But we would like Bitbucket even more friendly in that regard. Some PRs get really big and include multiple commits. It is really hard to keep context of all changes while doing review and it is easier to review commit by commit. The PR page has a "Commits" tab showing all commits. When you click on particular commit, you can see the diff and put comments there. The problem is that those comments are not considered to be part of PR and do not show up in Activities tab. If/when PR commits are rewritten to accommodate latests fixes based on other comments, all comments made to particular commit are lost and it is VERY hard to find them.

It would be nice if when you open commits from PR, they keep track that we are reviewing them as part of PR and thus all comments made there are considered part of PR (thus show up in Activities tab). You could have a special URL to view commit inside PR, e.g. /pull-requests/<PR_id>/<branch_name>/commits/<commit_id> in addition to usual commit URL /commits/<commit_id>.

Even if you do not rewrite Git history it would still be beneficial to see all comments to all commits under Activities tab.