Show comments in updated pull requests (BB-13964)

We use comments to review a pull request. After that we assign the Jira issue back to the developer to process the comments. We don't decline the pull request to allow updates.

After the updates from the developer the reviewer want to verify what has been changed based on his comments. But when the code lines change, the comments disappear. They are only visible on the "Activity" tab.

It would be much easier to check them if the comments are visible in the pull request view, for example in a drop down panel after click on the number of pull requests (currently this leads to the activity view).