Project cleanup, fix unit tests

 * Added [jspahrsummers/objc-build-scripts](https://github.com/jspahrsummers/objc-build-scripts) and [jspahrsummers/xcconfigs](https://github.com/jspahrsummers/xcconfigs)
 * Cleaned up the mess of project and target settings
 * Actually _run_ unit tests as part of CI – there was previously a critical Run Script build phase missing (trololo)
 * Fix broken tests reported by @randomsequence in 540dd95d31e6a2ac939033b052607c907ea97936