Updates to our issue status icons and colors

Our current issue icon colors are a source of constant user feedback, citing confusion with errors, confusion between why Open is green and Closed is red, accessibility concerns and the general scariness of seeing red across the issues index page when a bunch of closed issues is usually a good thing.

As part of our roadmap issue today we are starting a rollout that updates the issue closed icon from red to purple. Please see the roadmap issue for more information and future plans to address all of the feedback we have received.