Tax rules for USA

To extend the tax system to handle USA tax rates, we need to create rules at the sate level (and potentially further, down district or zip code).

Here's what I'm looking to implement to get started:
- Extend Tax Settings on Store edit page to capture administrative area (state)
- Add Product Variation Type reference to Tax Types (Allow for different rates on food vs clothes, etc)
- Create tax resolver to use appropriate tax rate per store and product