ISPN-4574 PartitionHandling: consider less than numOwners partitions

* Merge PartitionHandlingStrategy with RebalancePolicy -> AvailabilityStrategy
* Add a stable topology with the last topology that didn't need rebalancing
* NumOwnersNodeStopInSequenceTest - stop nodes gracefully instead of abruptly
ISPN-4574 PartitionHandling: consider less than numOwners partitions
I18N for the new error messages
ISPN-4574 PartitionHandling: consider less than numOwners partitions
Change access rules for unavailable mode
ISPN-4574 PartitionHandling: consider less than numOwners partitions

* Protect against null current/stable CacheTopologies reported by nodes on merge
* Add an Externalizer for CacheStatusResponse