Restore the "sip show users" and "sip show user" CLI commands

(closes issue #14180)
Reported by: amorsen
Patches:
      sip_show_users_161v3.diff uploaded by putnopvut (license 60)
Tested by: blitzrage, amorsen



git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@168610 65c4cc65-6c06-0410-ace0-fbb531ad65f3