Model misc_deduction historically

`misc_deduction` currently is not part of the federal income tax tree, nor does it have a formula. This could be due to it not counting for most cases any longer (see [this IRS publication](https://www.irs.gov/publications/p529#:~:text=recognize%20a%20child.-,Introduction,relating%20to%20unreimbursed%20employee%20expenses.)). We should try to add it to the tree somehow, even if via a list parameter that changes over time.

When we do this we should consider that Mississippi may apply this deduction differently from the US; see #2612.