New SIP Channel driver: Always Auth Reject

If no matching endpoint is found for the incoming request Asterisk will respond
with a 401 Unauthorized (rejecting the request), but will first challenge if
no authorization creditials are given.

Changes also included moving ACL options into a new global 'security'
configuration section in res_sip.conf.

(closes issue ASTERISK-21433)
Reported by: Matt Jordan
Review: https://reviewboard.asterisk.org/r/2554/


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@393442 65c4cc65-6c06-0410-ace0-fbb531ad65f3