added `keep_caller_id` option

Conflicts:
	applications/crossbar/priv/couchdb/schemas/clicktocall.json
	applications/crossbar/src/modules/cb_clicktocall.erl
set `keep_caller_id` to 'true' by default
explicitly set `caller_id_number` if defined, otherwise use `Contact`
update schema for `caller_id_number`