Issue: Cannot upload my own dataset

I look into `nlp-cli` and `user.py` to learn how to upload my own data.

It is supposed to work like this
- Register to get username, password at huggingface.co
- `nlp-cli login` and type username, passworld
- I have a single file to upload at `./ttc/ttc_freq_extra.csv`
- `nlp-cli upload ttc/ttc_freq_extra.csv`

But I got this error.

```
2020-05-21 16:33:52.722464: I tensorflow/stream_executor/platform/default/dso_loader.cc:44] Successfully opened dynamic library libcudart.so.10.1
About to upload file /content/ttc/ttc_freq_extra.csv to S3 under filename ttc/ttc_freq_extra.csv and namespace korakot
Proceed? [Y/n] y
Uploading... This might take a while if files are large
Traceback (most recent call last):
  File "/usr/local/bin/nlp-cli", line 33, in <module>
    service.run()
  File "/usr/local/lib/python3.6/dist-packages/nlp/commands/user.py", line 234, in run
    token=token, filename=filename, filepath=filepath, organization=self.args.organization
  File "/usr/local/lib/python3.6/dist-packages/nlp/hf_api.py", line 141, in presign_and_upload
    urls = self.presign(token, filename=filename, organization=organization)
  File "/usr/local/lib/python3.6/dist-packages/nlp/hf_api.py", line 132, in presign
    return PresignedUrl(**d)
TypeError: __init__() got an unexpected keyword argument 'cdn'
```

Comments:
It's my misunderstanding. I cannot just upload a csv. I need to write a dataset loading script too.

I now try with the sample `datasets/csv` folder. 

    nlp-cli upload csv

The error is still the same

```
2020-05-21 17:20:56.394659: I tensorflow/stream_executor/platform/default/dso_loader.cc:44] Successfully opened dynamic library libcudart.so.10.1
About to upload file /content/csv/csv.py to S3 under filename csv/csv.py and namespace korakot
About to upload file /content/csv/dummy/0.0.0/dummy_data.zip to S3 under filename csv/dummy/0.0.0/dummy_data.zip and namespace korakot
Proceed? [Y/n] y
Uploading... This might take a while if files are large
Traceback (most recent call last):
  File "/usr/local/bin/nlp-cli", line 33, in <module>
    service.run()
  File "/usr/local/lib/python3.6/dist-packages/nlp/commands/user.py", line 234, in run
    token=token, filename=filename, filepath=filepath, organization=self.args.organization
  File "/usr/local/lib/python3.6/dist-packages/nlp/hf_api.py", line 141, in presign_and_upload
    urls = self.presign(token, filename=filename, organization=organization)
  File "/usr/local/lib/python3.6/dist-packages/nlp/hf_api.py", line 132, in presign
    return PresignedUrl(**d)
TypeError: __init__() got an unexpected keyword argument 'cdn'
```


We haven't tested the dataset upload feature yet cc @julien-c 
This is on our short/mid-term roadmap though

Even if I fix the `TypeError: __init__() got an unexpected keyword argument 'cdn'` error, it looks like it still uploads to                                                                                                                               `https://s3.amazonaws.com/models.huggingface.co/bert/<namespace>/<dataset_name>` instead of `https://s3.amazonaws.com/datasets.huggingface.co/nlp/<namespace>/<dataset_name>`

@lhoestq The endpoints in https://github.com/huggingface/nlp/blob/master/src/nlp/hf_api.py should be (depending on the type of file):
```
POST   /api/datasets/presign
GET    /api/datasets/listObjs
DELETE /api/datasets/deleteObj
POST   /api/metrics/presign  
GET    /api/metrics/listObjs
DELETE /api/metrics/deleteObj
```

In addition to this, @thomwolf cleaned up the objects with dataclasses but you should revert this and re-align to the hf_api that's in this branch of transformers: https://github.com/huggingface/transformers/pull/4632 (so that potential new JSON attributes in the API output don't break existing versions of any library)

New commands are
```
nlp-cli upload_dataset <path/to/dataset>
nlp-cli upload_metric <path/to/metric>
nlp-cli s3_datasets {rm, ls}
nlp-cli s3_metrics {rm, ls}
```
Closing this issue.