Mark issues for which a pull request has already been opened

[david-cliqz]

It would be nice if, looking at the issue list, I could tell at first glance if a pull request has already been opened for a particular issue. All it would take is to mark it with a different color, or, preferably, a small pull request icon on the right side.

Even better, the icon could also have two variants: one when the pull request is against the default branch, and another, when it is not. In the latter case, it could be the same icon, only e.g. light grey instead of grey.

Alternatively, there could be a label assigned automatically; however, since projects are allowed to create and interpret their labels however they see fit, the icon approach would be better.