Implement pausing of continuous replication.

This results in creating the 1-replication so that the checkpointed_source_seq
can be restored.
Fix bugged logic generating local database tag.
Add forgotten import to use the api models for integrity agent.
Make querying _active_tasks compatibile with couchdb 1.2.2.

This version added string literal sufix in the replication_id in response format.
Fix wrong response for replication status.