Add regular expression filtering for manager events.

This patch as documented in the sample config allows one to optionally apply
white, black, or both types of filtering to manager events. The new
'eventfilter' option is set per user.

(closes issue #14861)
Reported by: fnordian
Patches: 
      eventfilter3.patch uploaded by fnordian (license 110),
      modified by me

Review: https://reviewboard.asterisk.org/r/673/


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@271868 65c4cc65-6c06-0410-ace0-fbb531ad65f3