ARI: Add support for Cross-Origin Resource Sharing (CORS), origin headers

This rejects requests from any unknown origins.

(closes issue ASTERISK-21278)

Review: https://reviewboard.asterisk.org/r/2667/


git-svn-id: http://svn.asterisk.org/svn/asterisk/trunk@394189 f38db490-d61c-443f-a65b-d21fe96a405b