iOS64 Unified API Support for Component Packaging (and Sample)

This should bring the repository up to where it needs to be for you to simply do a `cd Component && make package` to generate an iOS64 Unified API compatible Xamarin Component `.xam` file ready to upload to the store.

There's been a Sample added, as well as the packaging tools updated and component manifest updated to support `ios-unified` target.

Eventually you should be able to drop *Classic* API support and delete the old sample, etc, but for now, both are supported.