Mark Threads as Read/Unread

A common situation in review process is when the reviewer and the author discuss low-level decisions made in the code. The actionable units of review process are thus not comments, but threads. In the current UI, it's a pain for the pull request author to track threads that he has already done vs those that need to be done.

Raising issues in JIRA is not a solution: context is lost, and the process becomes more heavyweight. Most of the issues discussed are quite simple, so the overhead with entering an issue then transitioning it is not worth it.

A possible solution is read/unread markers on threads; ideal solution would include a place where unread threads are gathered.