Causal Regression Modeling

[psinger]

Adds new problem type causal regression modeling

Closes #495

Some code is duplicated, but decided to split it into two problem types.

[pascal-pfeiffer]

Awesome!

Can you look at the DS import quickly? I think it fails with the same issue that also fails in the test cases.

Else, code looks good to me! We probably want to extend docs, too, but that can be done in a subsequent PR.

[psinger]

That's weird, import works fine for me locally, will investigate.

For docs, where would we need to add it?

[psinger]

@pascal-pfeiffer ok should be fixed, wasnt pushed due to gitignore :)

[pascal-pfeiffer]

Working quite nicely, thank you!

Indeed, more documentation changes are probably not needed. Some suggestions/comments/questions in the code below.

[pascal-pfeiffer]

Thank you! lgtm