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: https://origsvn.digium.com/svn/asterisk/trunk@394189 65c4cc65-6c06-0410-ace0-fbb531ad65f3