Turn the example apps into templates and add a project scaffolder

[zantvoort]

The three storm-example-* repositories are clone-and-run, but nothing guides a new user to them as the starting point for their own project.

Mark the example repositories as GitHub template repositories, which adds the "Use this template" button at no cost, keep their pinned Storm version current on release, and link them from the README and docs.

The npm CLI scaffolder (storm new) is split out into #326.

Tasks:

• Mark storm-example-* as template repositories
• Release workflow keeps template versions current
• Link the templates from the README and docs