- Moved `BuildConfigurations` out of `Stripe` folder and into root directory
- Deleted unused xcconfig files (`LocalizationTester*.xcconfig` and `StripeiOSResources.xcconfig`)
- Migrated `StripeiOS`-specific build settings out of shared xcconfig files and onto the project.
- Added `clean_project_build_settings.sh` to ensure `project.pbxproj` files don't overwrite xcconfig settings (more below)
- Removed build settings from the StripeiOS target that were overriding xcconfigs (using `clean_project_build_settings.sh`)