Add header_dir to podspec

- update universal target to build dynamic target with static flag
- organize scheme order to match the target order

- add tests for new address API routes
- update BUYAddress data model to include an identifier property
- add BUYAddress API tests (without stubs, WIP)

- reduce poll iteration count
- change request URL for testing
- fix typo

- remove duplicate compile sources
- sync dynamic and static framework umbrella headers
- rename BUYClient+Checkout helpers category to avoid duplicate name

- add initializer to payment provider to inject fake safari controller