Standardize argument names

[benesom]

Do we prefer function argument name seperation with . or _? That is, response_call or response.call. We currently use both. For example, the ml_model R6 class uses predict.args and response.arg in its initialize method but the cate function uses response_model and propensity_model.

Is this something we would like to standardize?

[kkholst]

We should standardize, and I vote for response.call. For the cate function this is now addressed in #12

[benesom]

I also prefer dot seperation for argument names and snake case for functions and methods.