Add option to use gensim text keyword extraction and summarization

Gensim has a library for summarizing text and extracting keywords. It looks like it only works for english text because of the pre-processing (removing stopwords and stemming) that takes place. Look into whether we can use our own pre-processing algorithms using NLTK so we can support more languages. If not, we can just have the gensim algorithm as an option for english text. Look [here](https://radimrehurek.com/gensim_3.8.3/auto_examples/tutorials/run_summarization.html) for more details.