Refresh wsuwp-dev.sl state file

Would like to:

* [ ] Clean up documentation throughout to make things more obvious.
* [ ] Remove unnecessary `require` and `require_in` statements
* [ ] Remove the xdebug file management to be introduced in another issue.
* [ ] Remove the reliance on `wp-db-import`
* [ ] Use `wp` to setup the initial development environment if not yet available.