Avoiding deletion of all tagged events in rollback

[xirc]

This is required for #201.

rollback-tool-cassandra (v2.2.0) deletes all tagged events (events of tag_view) and rebuilds them:
https://github.com/lerna-stack/akka-entity-replication/blob/v2.2.0/rollback-tool-cassandra/src/main/scala/lerna/akka/entityreplication/rollback/cassandra/CassandraPersistentActorRollback.scala#L76-L77. The old events deletion feature deletes source events, which are required to rebuild tag_view completely. The rollback of tag_view has to be achieved while it avoids deleting all tagged events. This rollback might be achieved by updating tag-related tables (tag_view, tag_write_progress, tag_scanning): https://doc.akka.io/docs/akka-persistence-cassandra/1.0.5/journal.html#schema