Move "core" to a separate package, such as "cli-tools"

The `local-cli/core` is not really a core, it's just a set of useful "tools" that can be used to locate iOS project somewhere etc. 

In order to make it easy for other plugins and packages to use this, we should definitely make it a separate package with public interface. 

Right now, some developers are requiring them directly from "build" or "src" folder, which is dangerous.