CBG-2264: Set collection property on outgoing BLIP messages

[markspolakovs]

CBG-2264

Ensure that outgoing rev, norev, changes, getAttachment, and proveAttachment messages all have a collection property set if collections are in use.

Pre-review checklist

• [x] Removed debug logging (fmt.Print, log.Print, ...)
• [x] Logging sensitive data? Make sure it's tagged (e.g. base.UD(docID), base.MD(dbName))
• [x] Updated relevant information in the API specifications (such as endpoint descriptions, schemas, ...) in docs/api

Integration Tests

• [ ] gsi=true https://jenkins.sgwdev.com/job/SyncGateway-Integration/599/

[bbrks]

@markspolakovs this has picked up a conflict - but may make sense for @JRascagneres' branch to be merged first to avoid double-rebase