manager: ExtensionStatus event status human readable

Added a note in the changes file about the new 'StatusText' field that was
added to the 'ExtensionStatus' event.

(issue ASTERISK-23154)
Reported by: Jonathan Rose


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@406696 65c4cc65-6c06-0410-ace0-fbb531ad65f3