Change PR overview to be more like Gerrit

What does it mean to create a PR overview more like Gerrit?  I think that perhaps these things may help:

1. "compact" the Activity
2. Make the Activity chronological
3. Make the Activity threaded, if possible
4. Cumulative set of changes with each commit (more below on this one)

Take for example, a potential PR that has over 99+ comments and potentially has 10+ commits to the branch after the PR is opened and before it is merged or declined.  We need a way to follow the "discussion" that includes comments and commits.

Similar to Gerrit, if a commit occurs, it would be nice to also have some way of viewing the entire set of changes (cumulative) at that point in time – rather than just the delta of the commit.

The intent is to make this more user-friendly to developers familiar with Gerrit and the "mailing list" workflow that Gerrit provides.