Add basic non-citizen qualified alien statuses that grant eligibility for SSI

• To begin with, using section 2.a. of the SSI Program Operations Manual System (POMS): https://secure.ssa.gov/poms.nsf/lnx/0500502100
• There are a number of other exceptions not captured in this table but described elsewhere in the article, including veteran status, victim of DV, grandfathered status from 96, "Amerasian" status, timeframe from status granting, etc

Variable to add: is_ssi_qualified_noncitizen

I've attempted this change in this Fork: 0684b3d

It also:

• adds Param qualified_noncitizen.yaml (for the purposes of allowing simulations to new inclusions and exclusions in qualified noncitizens, e.g. DACA)
• adds Var ssi_40qq_earnings (a new bool Var for whether someone has 40 qualifying quarters of earnings, necessary for LPR to get SSI)
• amends Var immigration_status (adds new Enum values)
• amends Var is_ssi_eligible_individual