KAZOO-2351: remove unused clauses, update spec
KAZOO-2351: lookup original contact string for inclusion in MWI update
KAZOO-2351: track the original contact string, and allow queries for it

update specs
KAZOO-2351: permit the Original-Contact header in the query API
Merge pull request #315 from 2600hz/KAZOO-2351

Kazoo 2351