Add FreebaseQA dataset
This PR adds the FreebaseQA dataset: A Trivia-type QA Data Set over the Freebase Knowledge Graph

Repo: https://github.com/kelvin-jiang/FreebaseQA

Paper: https://www.aclweb.org/anthology/N19-1028.pdf


## TODO: create dummy data

Error encountered when running `python datasets-cli dummy_data datasets/freebase_qa --auto_generate`
```
    f"Couldn't parse columns {list(json_data.keys())}. "
ValueError: Couldn't parse columns ['Dataset', 'Version', 'Questions']. Maybe specify which json field must be used to read the data with --json_field <my_field>.
```
