Fix attachments missing from DocumentRevision

Retrieving a document via getAllDocuments returns document with their
attachments missing.
Fix document retrieval for getAllDocuments and getAllDocumentsWithIds
Add tests for attachments on objects retrieved from getAllDocuments and
getAllDocumentsWithIds
Merge pull request #50 from cloudant/33603_fix_missing_attachments

Fix attachments missing from DocumentRevision
Makes CDTAbstract/Pull/PushReplication conform to NSCopying.

This ensures that the replication configuration cannot change after
the instantiation of the CDTReplicator object, which could cause some
bugs.