Make a couple of changes to help AMI events to be more clear in what is occurring.

* BridgeEnter now contains the unique ID of the channel that is to be swapped out, if applicable.
* There is a ParkedCallSwap event that is sent when a parked channel has a new channel take its place.

(closes issue ASTERISK-22193)
reported by Mark Michelson

Review: https://reviewboard.asterisk.org/r/2712



git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@396107 65c4cc65-6c06-0410-ace0-fbb531ad65f3