ENH: Remove hard-coding of SGB II age groups

[hmgaudecker]

Is your feature request related to a problem?

arbeitsl_geld_2_kindersatz_m_hh_ab_2011 currently does:

        arbeitsl_geld_2_params["regelsatz"][6] * anz_kinder_bis_5_hh
        + arbeitsl_geld_2_params["regelsatz"][5] * anz_kinder_ab_6_bis_13_hh
        + arbeitsl_geld_2_params["regelsatz"][4] * anz_kinder_ab_14_bis_17_hh
        + arbeitsl_geld_2_params["regelsatz"][3] * anz_kinder_ab_18_bis_24_hh

Similarly, #582 introduced hard-coded 25s in groupings.py

Describe the solution you would like to see

Include mappings of regelbedarfsstufen to min/max ages. In the above code snippet, work at the individual level.

[MImmesberger]

In this context, I'm wondering how we understand the relation of alleinerz and the Einstandspartner. Does p_id_einstandspartner>0 imply not alleinerz (if there are any children of course)? I think it does.