[Informal] Migration to Apache Isis 2.0.0

[andi-huber]

I've added a new module to Apache Isis Core (master branch), to ease the Migration from 1.16.x to 2.0.0.

Among others, it provides a transitional implementation of the DomainObjectContainer, which was removed in 2.0.0.

We will most likely provide this new module as 'do-not-use-in-production', but nevertheless, it might help through the migration process. Feel free to contribute to this new module at your convenience.

Location: /core/legacy/transition-1-2
Add as a dependency:

<dependency>
    <groupId>org.apache.isis.core</groupId>
    <artifactId>isis-core-transition-1-2</artifactId>
    <version>${isis.version}</version>
</dependency>