ARI: Add debug logging for events and responses

This adds DEBUG level logging for ARI websocket events and HTTP
responses similar to what is available for AMI. Logging for ARI HTTP
requests is already adequate for debugging purposes.
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Merged revisions 412565 from http://svn.asterisk.org/svn/asterisk/branches/12


git-svn-id: http://svn.asterisk.org/svn/asterisk/trunk@412566 f38db490-d61c-443f-a65b-d21fe96a405b