Pull Request border change

Changed border from 'number of Pull Requests' to 'total number of days all open Pull Requests have been open for'.

*Do not merge this yet.* On testing, we currently have a border that is *236px* wide. We should look at closing the long-running pull requests before we merge this (which is kind of the point of this change).

- [ ] Code Review
- [ ] Clear long-running pull requests