Impute wealth from SCF for consumption tax transition

[MattHJensen]

When we model a consumption tax using the sources method we will need wealth data from the SCF to distribute the transition burden. Additionally, we may want a path of savings/dissavings so that we can distribute the transition burden across years.

Useful docs

• TPC: Methodology for distributing a VAT
• TPC: Estate tax model
• TPC:Estate tax model 2 - appendix A is very helpful

This is moved from PSLmodels/Tax-Calculator#224