HST should not bootstrap 'localhost' CMS mount

Discussed with Ard: currently, HST's site configuration does not bootstrap a dev-localhost/localhost mount for the a site, but the HST's platform configuration does always bootstrap a dev-localhost/localhost CMS mount. This is asymmetric, and ugly if the project does not want to bootstrap this configuration into a production environment.

The intent is therefore to move the definition of the dev-localhost hosts-group out of HST's platform configuration and into the archetype's repository-data module, much like the archetype's hst-site module bootstraps the same hosts-group for the site mount.

This implies that existing 13.0 projects (demos, connect, hap etc) need to be changed, too.