Update to gensim 4.0

[combedhadgehog]

Some adoptations are needed to run under new version of gensim:
1)
from word2vec.Word2Vec.load_word2vec_format
to KeyedVectors.load_word2vec_format
2)
from model.vocab and model.vocab.keys()
to model.index_to_key
3)
from model.vocab[w].index
to model.key_to_index[w]
4)
from model.syn0 = np.delete(model.syn0, indices_to_delete, axis=0)
to model.index_to_key = np.delete(model.index_to_key, indices_to_delete, axis=0)
model.vectors = np.delete(model.vectors, indices_to_delete, axis=0)
5)
from word2vec.Word2Vec.load_word2vec_format
to KeyedVectors.load_word2vec_format