Add JustCause as a toolbox for evaluation

[MaximilianFranz]

Proposing to add JustCause to the list of toolboxes in my own interest as a co-author.

JustCause aims to simplify and standardise the evaluation of causal effect estimation methods, which I found in my thesis to be an error prone and non-trivial task given the importance of the underlying data generating processes.

JustCause:

• Provides common reference datasets (IHDP, Twins, ACIC challenge) in an accessible way
• Provides a method for generating synthetic data from a standardised terminology
• Provides basic learners and methods.

In the future we hope to add more learners as well as further datasets and are looking for contributions from researchers.

[rguo12]

Yes, we should add more datasets especially considering the evaluation of causality related areas is not that solid in current stage.