Start update drive to IPython API modifs.

https://github.com/ipython/ipython/pull/6982 is needed not to crash the notebook server by actually requesting contents on the backend.

Current IPython notebook that are on drive and are stored as version v3 will not work since IPython's javascript now only handle notebook format v4, and with standard content manager, the conversion is made from read to disk. 

I guess we will have to write a converter in js too. 
This code needs to be something like
```
.then(function(file_id) {
  return gapi_utils.execute(gapi.client.drive.files.delete({'fileId': file_id}));
});
```

gapi... methods return request objects, which still need to be executed.

gapu_utils.execute wraps such a request object in a promise, catching errors.