New feature: AMI Action FilterAdd

This adds a new action, FilterAdd to the manager interface that allows control over event filters for the current session

(closes issue ASTERISK-16795)
Reported by: kobaz
Tested by: kobaz,loloski



git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@326267 65c4cc65-6c06-0410-ace0-fbb531ad65f3