Changes

Implement model deletion in the Model Manager

The model manager API provides a deletion method, but this was not implemented. This commit implements deletion logic, which delegates to the Model Nexus. The Model Nexus:

1. Finds the Model
2. If found it deletes any and all providers using the model, then it deletes the model from its owning EPackage
3. If the EPackage is now empty of models then the EPackage is removed from the Model Nexus

The ModelImpl has also been updated to check the the model is still registered before allowing any action. This prevents deleted models from being used after they are deleted.

Signed-off-by: Tim Ward <timothyjward@apache.org>
 (commit: d221b61)

Expose #getProviders(String modelPackageUri, String model) from the twin

The method getProviders(String, String) existed in the EMF Twin, but not the base twin. As we already use the model package uri extensively in that interface we should expose it here as well.

Signed-off-by: Tim Ward <timothyjward@apache.org>
 (commit: 6eebd84)