Generator: Implement Composition as abstract class to inherit redundant fields for other Compositions

[SevKohler]

Background

Currently many of the generated Compositions contain duplicated fields like Language, these Attributes could be contained by a root class Composition, which makes specific Compositions smaller and allows easier handling of Compositions when programming. Especially when in general Compositions are to be referenced.

Acceptance criteria

Implement (abstract) class Composition that contains all Attributes that are standard to every Composition.

Success criteria

• Review / Merge request approved (P2P session)
• Unit tests passed
• Updated documentation (Javadoc and Sphinx)
• Acceptance criteria fulfilled
• Build without errors
• Release notes prepared
• Runtime warnings

[ppazos]

I think we can have an AbstractComposition in the shared package that all generated Composition DTOs inherit from.

[subigre]

+1 I would appreciate if we might have this abstract Composition class.
This could help to implement the FHIR Bridge and the openEHR components for Camel having something similar to the MessageConverter provided by Spring for JMS.

[subigre]

One additional comment, it might be interesting to update the CompositionEndpoint:

public interface CompositionEndpoint {

    <T extends Composition> T mergeCompositionEntity(T entity);

    <T extends Composition> Optional<T> find(UUID compositionId, Class<T> clazz);
}

[SevKohler]

This depends on the Composition, if we have fields that are contained in every Composition, because of the Reference Model, it is better to use an Abstract Class (if not we have to duplicate them). If not i agree on the solution above.

[stefanspiska]

Fixed in #153 which will become release 1.0.0
see
https://github.com/ehrbase/openEHR_SDK/blob/release/v1.0.0/CHANGELOG.md for changes
https://github.com/ehrbase/openEHR_SDK/blob/release/v1.0.0/UPDATING.md for how to update