Expose the execution state of a model in a generic fashion

Exposing the execution state of a model in a generic fashion similarly to the trace has several benefits:
- avoids the need to have a merged static+dynamic ecore metamodel, and this avoids the need to manage an "extends" relationship between two ecore files (https://github.com/eclipse/gemoc-studio/issues/58)
- this also allows writing sirius java services that would display the RDT
- applied to K3 with runtime data, this would simplify the debug of the k3 code since we do not have the aspect copy (currently, the aspect copy of Melange prevents eclipse from correctly linking to the real K3/xtend source when launching the second eclipse workbench in debug mode)