[#843] Add status: unclaimed / status: claimed automatically

* only to type: issue, not type: pull request

* when the issue is opened, apply the claimed/unclaimed status

* when a comment is made on an issue, update the claimed/unclaimed status
  if it's been changed without our noticing (may have been selected via
  the dropdown, for example), and make sure to automatically add the
  claimed/unclaimed status if the labels have been edited
tmp