Add transfer support to CEL

This adds CEL support for blind and attended transfers and call pickup.
During the course of adding this functionality I noticed that
CONF_ENTER, CONF_EXIT, and BRIDGE_TO_CONF events are particularly
useless without a bridge identifier, so I added that as well.

This adds tests for blind transfers, several types of attended
transfers, and call pickup.

The extra field in CEL records now consists of a JSON blob whose fields
are defined on a per-event basis.

Review: https://reviewboard.asterisk.org/r/2658/
(closes issue ASTERISK-21565)


git-svn-id: http://svn.asterisk.org/svn/asterisk/trunk@394858 f38db490-d61c-443f-a65b-d21fe96a405b
Add CEL local optimization record type

This adds a new CEL event type, AST_CEL_LOCAL_OPTIMIZE, to represent
local channel optimizations. Local channel optimizations were one of
several things conveyed by the now defunct BRIDGE_UPDATE event type.
This also adds a unit test to test generation of this new CEL event.

Review: https://reviewboard.asterisk.org/r/2676/


git-svn-id: http://svn.asterisk.org/svn/asterisk/trunk@394870 f38db490-d61c-443f-a65b-d21fe96a405b