[NATIVESDK-187] Add shared Xcode schemes.

This PR resolves [NATIVESDK-187](https://jira.appcelerator.org/browse/NATIVESDK-187) by providing the APSHTTPClient Xcode project with a set of shared schemes (i.e. not per-user schemes) so that the project as a whole has a common set of targets to build, configurations to use when building, and a well defined collection of tests to run.