Build PHL Homestead Benefit

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Related to Issue #32

You can be eligible for LOOP, but if may be more advantageous to either apply for, or keep if you have it already, the Philadelphia Homestead Exemption instead. There are no financial eligibility requirements for the Homestead Exemption, such as income or resource limits.

• [x] Add homestead to benefits.dmn
• [x] Add lives in philadelphia decision service from location.dmn
• [x] Add not enrolled in homestead to enrollments.dmn. Even if already enrolled, we want to return an estimated property tax amount with Homestead, to use in comparison to the LOOP tax freeze amount.
• [x] Add Homestead Exemption related housing rules to housing.dmn
• [x] Create tests and get them to pass

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Benefit amount updates will be done in future tickets, including comparing Homestead to LOOP freeze amounts.