Refactor PhlSeniorCitizenTaxFreeze to use new checks

This wires up the following checks to the SCTF library benefit:
- OwnerOccupant
- LivesInPhiladelphiaPa

The remaining eligibility check for this is a complex age requirement.  It is implemented in the SCTF library benefit DMN. I intend to implement it as a custom check as part of #339 .

The complex age requirement raised some interesting questions about how to implement similar checks in the future. We will likely eventually need to have better solutions for:
- How might we share data facts between library and custom checks?
  - We discussed possibly using the same "situation" input across library and custom checks.
  - We also discussed finding a way to use the same data shape for all three of: custom checks/form editor/library checks
  - Another related feature that will help: supporting library benefits in the web app. This is another route to allowing users to bypass complex/bespoke benefit logic.
- How might we access library checks from within custom checks?
  - There are a few different approaches from backend and UX standpoint we could take with this
  - This is probably blocked until we figure out the data sharing question

I'm punting/letting go of the above questions for now because of two recent realizations:
- In the set of 5 property tax relief benefits, there are no age-related requirements except for SCTF. So, we don't need to solve the data-sharing question right now.
- There is a simple enough workaround to sharing data between custom and library checks that I wasn't considering before: mapping data in the form editor using the Expression Component (e.g. setting `custom.clientDateOfBirth` to `people.client.dateOfBirth`). Ideal? No. But simple enough that I think it buys us time to finish the Prototype v2 milestone, get this in front of users, and prioritize a long-term solution based on their feedback.

Author: prestoncabe