Added language detection for spans to the pipeline
In language_identifier.py I have implemented the spacy_fastlang module in order to detect languages for small bits of text (sentences). For simple testing purposes, I've refactored the -dev flag in promethia.py to keep the detection as isolated as possible. Lastly I've added the 'spacy_fastlang==1.0.1' to requirements.txt to make it installable.