* Make batchwise adding of evaluation data possible
* Fix typos in docstrings
* Merge add_eval_data and add_eval_data_batchwise
* Improve import statements
* Move add_eval_data to BaseDocumentStore
* Add batch_size param to write_documents and write_labels in EsDocStore
* Adjust docstring
Co-authored-by: Malte Pietsch <malte.pietsch@deepset.ai>