Add a built-in configuration dictionary for machine learning with text data

We can support machine learning with text data in TPOT by adding the [CountVectorizer](http://scikit-learn.org/stable/modules/generated/sklearn.feature_extraction.text.CountVectorizer.html) and [TfidfVecorizer](http://scikit-learn.org/stable/modules/generated/sklearn.feature_extraction.text.TfidfVectorizer.html#sklearn.feature_extraction.text.TfidfVectorizer) to a separate built-in configuration dictionary. I don't think we would need to change any of the other operators.

Unfortunately, without a pipeline grammar we can't force those vectorizers to always be at the beginning of every pipeline, but I suppose for text classification problems all of the pipelines that don't have one of the vectorizers will go "extinct."

Thoughts?

cc @weixuanfu2016 @teaearlgraycold