Make model loader more tolerant regarding unknown types
The consolidation of the AF3 main products plugins will likely result into a larger number of unknown model types since a number of metamodels will be removed.
Instead of keeping this metamodels just to write a migrator that removes
the respective model elements, the model loader in the kernel (i.e.
ModelContext) should be made more tolerant:
- Loading a model with elements that have unknown types should not result into an error, but the respective elements should be removed
- In such a case, an warning should be logged (important to warn developers of undesired changes)
Test cases: models from AF3 2.16 release (note: the example models shipped with AF3 have been adjusted in #3861). In particular:
In the frame of this ticket, also the code for importing a model from the menu, loading an example from the file menu and loading a model from the workspace should be made more consistent.
(from redmine: issue id 3865, created on 2019-11-05, closed on 2019-12-20)