Fix CORS in devhub test receipts (bug 1104371)

This also fixes the CORS decorator which was
previously broken for OPTIONS requests.
Merge pull request #2786 from kumar303/dev-cors

Fix CORS in devhub test receipts (bug 1104371)
add in desktop payments flag (bug 1109191)
Merge pull request #2788 from andymckay/1109191

add in desktop payments flag
add a contribute.json file (bug 1074452)