ISPN-3885 Non-Tx Cross Site optimizations

* clear() and putAll() methods remain unchanged
* fixed a link and a list in the x-site documentation
* for single key write command, the primary owner will send to
the backup site when it has applied the data locally.
ISPN-4018 Write skew should not be check if conditional operations does not change the value
ISPN-4024 Cross-Site State transfer: alpha version

Cross-Site Replication State Transfer in a stable topology,
i.e. no nodes leaving or joining during the state transfer.