32818 add attachments

- Added attachment handling to CDTMutableDocumentRevision via the attachments property
- Depercated old attachment API in CDTDatastore+attachments.h
- Created new Attachment CRUD tests based off AttachmentCRUD.m
You should check whether the attachment is already saved, and if so, don't call streamAttachmentToBlobStore. Currently you're re-checking the SHA-1 for all the saved attachments which could be expensive.

A test like [attachment isKindOfClass:[CDTSavedAttachment class]] would do the trick.