Support for `lifelines`

[s3alfisc]

lifelines is the most comprehensive Python package for duration modeling: link

[dsliwka]

@s3alfisc: I have added a first version of a lifelines extractor. In the process I have also added a function inspect_model to which a user can pass any model for which an mtable extractor exists and the function shows all coefficient specific stats and model stats that are extracted and can be displayed with ETable. This is not yet fully documented, but an example is shown here:.