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: http://svn.asterisk.org/svn/asterisk/trunk@406696 f38db490-d61c-443f-a65b-d21fe96a405b