Support creating Flutter projects for new "skeleton" template #3554

-t, --template=<type>        Specify the type of project to create.

          [app]              (default) Generate a Flutter application.
          [module]           Generate a project to add a Flutter module to an existing Android or iOS application.
          [package]          Generate a shareable Flutter project containing modular Dart code.
          [plugin]           Generate a shareable Flutter project containing an API in Dart code with a platform-specific implementation for Android, for iOS
                             code, or for both.
          [skeleton]         Generate a List View / Detail View Flutter application that follows community best practices.