text: Title: Investigate Usage of sklearn VectorizerMixin with DispersionPlot Visualizer
  Body: **Describe the solution you'd like**
  It was proposed that we investigate the sklearn.feature_extraction.text. VectorizerMixin. This will make this DispersionPlot visualizer more like a Scikit-Learn text transformer, and will allow us to submit input as:
  
  - list of words
  - raw string that is tokenized using sklearn
  - list of strings representing documents on disk
  
  More information on the Mixin can be found here:
  https://github.com/scikit-learn/scikit-learn/blob/a24c8b46/sklearn/feature_extraction/text.py#L98
  