Implement a table for returning all parameters from fitABN

- have a consistent class for all model types in fitABN
- generate and return a nice and neat table, including all parameters for the DAG (make it relative, such that all node/arc combinations are possible)
- make sure it also works for mixed-effect models
- maybe also return a tex file for latex tables directly (e.g., such as biostatUZH::tableRegression())