Previews are not reset properly when uploading new version

When uploading a new version of a PDF, we immediately fetch the content profile again. This is part of the response:

```
    "previews": {
        "pageCount": 2,
        "status": "done",
        "total": 8,
        "thumbnailUri": "local:c/cambridge/PT/Xs/O1/fK/PTXsO1fKkf/previews/1368202781746/thumbnail.png",
        "thumbnailUrl": "/api/download/signed?uri=local:c/cambridge/PT/Xs/O1/fK/PTXsO1fKkf/previews/1368202781746/thumbnail.png&signature=06e039c01b6d894bb9245124e79404a51919dd08&expires=1368204300000"
    },
```

It looks like the pageCount, status, total and thumbnailUri/ls are not being reset properly straight away, making it not possible for the UI to generate a correct preview. Also, it would probably be easier if the `uploadNewVersion` endpoint would return the new content item's basic profile straight away.

This ticket follows up on sakaiproject/3akai-ux#2731