Initial implementation of Observe and Store with durability checks.

//check for master persistence
 var result = client.ExecuteStore(StoreMode.Set, "foo", "bar", PersistTo.One);

 //check for master persistence with replication to 2 nodes
 var result = client.ExecuteStore(StoreMode.Set, "foo", "bar", PersistTo.One, ReplicateTo.Two);

Multi-node persistence/replication checks fail sporadically on observe.