deleted NGramGenerator in favor of RestrictedNGramGenerator

RestrictedNGramGenerator can be initiated with '' for the surface forms file,
which results in similar behavior as NGramGenerator, but with Spotlight
tokenizers.

*BUT* the behavior is different: see failing test!
re-factored RestrictedNGramGenerator

- variables to refer to distributed cache files inside and outside of getCacheFiles()
- Bugfix: loading of tokenizer model with correct variable and in exec()
- some formatting