BUG: Mostly replace `eink_st` / `soli_st` by `lohn_st` / `soli_st_lohnst`

[hmgaudecker]

Bug description

We have been using eink_st / soli_st to get at proxies for net income in several places.

Probably this should change to a combination of lohn_st / soli_st_lohnst as this is what is actually considered in many cases.

However, things may need a different treatment if income other than from dependent employment is around. Sometimes there will be a complete regime change, e.g., for Elterngeld the reference period changes from a 12-months window before birth to the calendar year before birth.

[hmgaudecker]

Just stumbled across this in grunds_im_alter, but will be relevant in many other locations. Best search for eink_st.

[hmgaudecker]

@JakobWegmann, would be great if you could weigh in here.

Often, the strategy will likely be to have an input column with relevant net income from the previous year and giving people advice on how to generate it if they have the previous year's data.

[JakobWegmann]

I think eink_st / soli_st should be replaced by lohn_st / soli_st_lohnst in the following functions:

• arbeitsl_geld_eink_vorj_proxy_m (Vorjahr input names and their namespaces #1040)
• elterngeld_nettolohn_m (Update Elterngeld #756)
• wohngeld_eink_vor_freib_m_mit_elterngeld
• arbeitsl_geld_2_eink_m
• grunds_im_alter_eink_m

This is quite a substantial change, so it would be good to have many solid test cases, optimally also spanning the last years.

• For unemployment benefits the official calculator can be used to obtain test cases for the last years
• To obtain test cases for parental leave benefit I contaced the ministry a year ago, but they could not provide me any. There are, however, numerous inofficial calculators in the internet, so that should be ok
• For the other transfers I'm not aware of any good test cases
• For housing allowance test cases would be extremely helpful, because I'm not 100% sure how the law is interpreted. On some homepages it sound as if the (at least nicht-pauschalisierte) Lohnsteuer is irreleant, e.g., here: https://www.wohngeld.org/wohngeldgesetz-wogg/paragraph16/

[hmgaudecker]

I am actually not sure about the last three items on the list -- at least we would need to check what happens for people with income from other sources.