Add features for taxable income (zve function)

[MaxBlesch]

• [ ] Model all seven income sources separately. This means to split the current gross_e1 to differentiate between income from farming, business, self-employment and freie Berufe.

• [x] If this is done, check which income sources are relevant for which benefits (Elterngeld, ALG I, Wohngeld, ALG II,...). Edit: This is obsolete as you don't need the income definitions from the income tax, but rather the actual gross incomes (e.g. self-employment and employment income for Elterngeld)

• [ ] Lohnsteuer: Model withholding tax depending on Steuerklasse. (see also #18)

• [ ] Progressionsvorbehalt: There are a couple of income items (e.g. Elterngeld, Unemployment Benefit) which are not taxed, but they increase the individual tax rate. Not yet modelled. (see #126)

• [ ] Taxable Income: Model the most important deductions (fiscal-wise), e.g. Entfernungspauschale, Unterhaltsfreibetrag.

[hmgaudecker]

Still relevant / any progress?

[Eric-Sommer]

still relevant

[hmgaudecker]

This is horribly outdated, no use in keeping it open.