33661 update conflict handling

Update conflict handling to enable the use of CDTMutableDocumentRevision as a conflict resolution.
Some documentation - what does this test resolver do? It looks like it:
- Merges all of the keys from the documents (last one wins if they key is defined in multiple documents?)
- Merges all of the attachments
- Optionally adds a new attachment
- Optionally picks a parent revision
Is this right?