* Sharding only within own team (coordinator is singleton)
* the ddata Replicator used by Sharding must also be only within own team
* added support for Set of roles in ddata Replicator so that can be used
by sharding to specify role + team
* Sharding proxy can route to sharding in another team
* fix merge issues of DataEnvelope and its pruning
* simplify by removing the tombstones, which didn't work in all cases anyway
* keep the PruningPerformed markers in the DataEnvelope until configured
TTL has elapsed (wall clock)
* simplify PruningState structure
* also store the pruning markers in durable data
* collect removed nodes from the data, listing on MemberRemoved is not enough
* possibility to disable pruning altogether
* documented caveat for durable data