Batch the variant data into a single request

Fixes #28

Signed-off-by: Ryan O'Hara <oharar@email.chop.edu>
This should be checked first to ensure the `ids` key exists otherwise it's an invalid request body.

```python
if 'ids' not in request.data or not isinstance(request.data['ids'], list):
    return self.render({'message': 'An array of "ids" is required'},
                       status=codes.unprocessable_entity)
```