Error in Demo for Specific Datasets
Thanks for reporting these errors :)

I can actually see two issues here.

First, datasets like `natural_questions` require apache_beam to be processed. Right now the import is not at the right place so we have this error message. However, even the imports are fixed, the nlp viewer doesn't actually have the resources to process NQ right now so we'll have to wait until we have a version that we've already processed on our google storage (that's what we've done for wikipedia for example).

Second, datasets like `newsroom` require manual downloads as we're not allowed to redistribute the data ourselves (if I'm not wrong). An error message should be displayed saying that we're not allowed to show the dataset.

I can fix the first issue with the imports but for the second one I think we'll have to see with @srush to show a message for datasets that require manual downloads (it can be checked whether a dataset requires manual downloads if `dataset_builder_instance.manual_download_instructions is not None`).

 I added apache-beam to the viewer. We can think about how to add newsroom.  We don't plan to host the source files of newsroom ourselves for now.
You can still get the dataset if you follow the download instructions given by `dataset = load_dataset('newsroom')` though.
The viewer also shows the instructions now.

Closing this one. If you have other questions, feel free to re-open :)
Selecting `natural_questions` or `newsroom` dataset in the online demo results in an error similar to the following.

![image](https://user-images.githubusercontent.com/60150701/85347842-ac861900-b4ae-11ea-98c4-a53a00934783.png)
