MB-12750 proxy xdcr replications rest api to goxdcr

the following api's

- GET /settings/replications
- GET /settings/replications/replication_id
- POST /settings/replications
- POST /settings/replications/replication_id
- POST /controller/createReplication
- POST /controller/cancelXDCR/replication_id
- DELETE /controller/cancelXDCR/replication_id

Change-Id: I921f64c642fa63cba2544129e359b3da645bc308
Reviewed-on: http://review.couchbase.org/44297
Tested-by: Artem Stemkovski <artem@couchbase.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>