Meta Models core extensions (Decorators + custom logic)

[salaboy]

Decorators and currently working adding extra information that can be maintained in a different data source from where the tasks are persisted and handled.
This meta information can be extended and customized for multipurpose behavior.

We need to refine the decorator mechanism and contexts to improve usability. We need to include also a registry to have a default set of decorators that will be usually needed in runtime and simple and transparent configurations mechanisms.