Changes the CDTReplicator -start signature.

-(void)start becomes -(BOOL)start:NSError** and -start is deprecated.

Errors created by TDReplicator objects are propaged from
TDReplicatorManager. They are reported to the Log (via Warn),
but new CDT-level errors are reported to developers using the
CDT API.
Adds tests to ensure that the correct type of TDReplicator is created
by a TDReplicationManager when using the NSDictionary object produced
by the CDT*Replication objects.
Merge pull request #47 from cloudant/32779-change-CDTReplicator-start-signature

Changes the CDTReplicator -start signature.