Add `Dataset` methods and init utility function for fields

[xroynard]

Make similar functions to:

• initialize_dataset_with_tabular_data
• Dataset.add_tabular_scalars
• Dataset.get_scalars_to_tabular

But for fields instead of scalars

Checks should be done to verify that provided fields have the same shape for all samples, else return a ShapeError

[xroynard]

Will be solved by #106 for:

• Dataset.add_tabular_fields
• Dataset.get_scalars_to_fields

Simultaneously, similar methods will be implemented for time_series in #106

[xroynard]

Will be done in #101, with standardization of features