Add Library Checks for Property Tax Benefits

[prestoncabe]

As a Benefits Analyst
When I create a new benefit or manage an existing benefit
Then I should have access to the complete set of eligibility checks needed to recreate the property tax relief screener at https://phillypropertytaxrelief.org.

[prestoncabe]

I began doing some experimentation with how we might change the "situation" (JSON input to the API) to conform to how #271 changed the format (similar to OpenFisca's web API). Nothing definitive so far, but I am leaning toward believing that a way forward could be to implement the OF country template in Java/DMN, and make the web API 100% (or as close as possible) compatible with the OF web api for the template, then add the property tax benefits to the template (and probably refactor to remove the examples from the template)... unsure if this would be an immediate pivot, or just something to keep in mind for after Prototype v2.