Add quora dataset
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Tests seem to be failing because of pandas Kaggle needs authentification to download datasets. We don't have a way to handle that in the lib for now
Added the [Quora question pairs dataset](https://www.quora.com/q/quoradata/First-Quora-Dataset-Release-Question-Pairs).

Implementation Notes:
- I used the original version provided on the quora website. There's also a [Kaggle competition](https://www.kaggle.com/c/quora-question-pairs) which has a nice train/test split but I can't find an easy way to download it.
- I've made the questions into a list:
    ```python
    {
        "questions": [
            {"id":0, "text": "Is this an example question?"},
            {"id":1, "text": "Is this a sample question?"},
        ],
    ...
    }
    ```
    rather than:
    ```python
    {
        "question1": "Is this an example question?",
        "question2": "Is this a sample question?"
        "qid0": 0
        "qid1": 1
    ...
    }
    ```
    Not sure if this was the right call.
- Can't find a good citation for this dataset
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