Cannot start server without installing all support libraries

[reckart]

Describe the bug As far as I remember, when I wanted to start the server with just space, I had to comment out all the classifiers classes from the init file in the contrib package that were not spacy because during the loading of the init file, Python would try to resolve the imported classes and fail trying to do that (because the dependencies from the other classifiers were not installed).

[reckart]

Also affects the tests. When running the tests, those tests for which the dependencies are not fulfilled should probable by skipped.