module `data_loader` is not being used (?)

[rafaelpadilla]

During this discussion I realized the data_loader module consists of a single function load_csv, which is a wrapper of pandas.read_csv(..._).

However, this function seems to be used only in the notebook and a test below:

• 3W/docs/notebooks/load_csv_usage_examples.ipynb
• /tests/test_data_loader.py
  

We need to:

• Make sure the module toolkit/data_loader is not needed anymore
• Remove the whole module, the notebook, the tests and every part related to it.