Add handling of a users JSON file to limit whose PRs are shown
Add handling of a users JSON file to limit whose PRs are shown

- In the Core Team we have around fifty repos to keep track of pull
  requests on, but only nine or ten contributors directly in the team.
  To avoid everyone's PRs for every one of those repos coming up and
  us struggling to scan the list to find relevant ones, we've added
  handling for a configurable `users` file optionally included in the
  gist.
- Test gist available at: https://gist.github.com/issyl0/70cf0c8f3d0b1ccd2f6e.
- We (Alice Bartlett and I) didn't do this in the BackboneJS "way".
  Instead we put a global `users` array at the top of the file, but
  it was the way that we found that worked.

HolyHaddock/fourth-wall,HolyHaddock/fourth-wall,Wynndow/wynndow.github.io,alphagov/fourth-wall,dxw/fourth-wall-for-gitlab,dxw/fourth-wall-for-gitlab,Wynndow/wynndow.github.io,alphagov/fourth-wall,dxw/fourth-wall-for-gitlab,HolyHaddock/fourth-wall,alphagov/fourth-wall,Wynndow/wynndow.github.io