Why do we check for "Revision" in vocabularies.managers?

`Revision` does not seem to exist in the dict keys and the situations in `geospaas.vocabularies.managers` are not tested. 
```
if 'Revision' in platform.keys():
    continue
```
I.e., the second line is not tested.

- [ ] Check if this is really needed

- [ ] Add unit tests for these situations