Tweak the github bot labelling behavior

* newly created issue with labels attached (for admins with sufficient
  privs) should keep the labels

* curated: beginner / curated: mostwanted should be among list of
  addable labels
Merge pull request #84 from afuna/tweak-labels

Tweak the github bot labelling behavior
Merge branch 'release-1.22' into develop

* release-1.22:
  Tweak the github bot labelling behavior