[PP-1] Introduce a VersionedSchema object to hold multiple versions of a database Schema definition

Problem/Motivation

Database updates require multiple versions of a Schema object, one for each incremental update. Currently the update functions just pass the increments, but it's difficult then to keep track of what each version looks like overall. With the introduction of the SchemaDefinition API this also looks weird.

Having an object that holds multiple versions of the Schema and returns either the latest or a specific one seems could fit this need in a nicer way. Also, in the future diffrent version of the same Schema could be diffed to identify automatically the changes that occur and make the sync of the actual db implementation with the abstract definition less manual.

Proposed resolution

Remaining tasks

User interface changes

Introduced terminology

API changes

Data model changes

Release notes snippet