Various fixes for the JSON-relational mapper

* Update EventCapsule schema to 8326736.
* Infer uniqueness of UUID from the property's format specifier.
* Factor out column sort into separate function.
* Make deeply-nested properties sort after shallow-nested ones.
* Fix nullable constraint detection.

Change-Id: I36002e62f570f418bd59dd1fb5ace2a23514b098
Merge "Various fixes for the JSON-relational mapper"