Command-line interface (Epic)

In #118, we started working on a command-line interface to generate app scaffolds, allowing users to select a more elaborate setup in addition to the existing simple React app template.

These are the steps I believe we need to complete before considering the CLI tool ready:

* [x] Merge the CLI setup from #118
* [x] Replace the root folder with the `/cli` contents
* [x] Add package versioning workflow

Some features suggested by @AliceR that don’t exist yet but would be good to have:

* Accessibility (a11y) instrumentation
* [x] Git hooks

I believe these are heavier lifts and could be tracked separately for a subsequent release.

cc @danielfdsilva @dzole0311