Rename the file to match its ID, add developer tag, and extend the
description. This fixes all issues with `appstreamcli validate`:
> I: org.cockpit_project.starter_kit:10: description-first-para-too-short
> Scaffolding for a cockpit module.
> I: org.cockpit_project.starter_kit:~: developer-info-missing
> W: org.cockpit_project.starter_kit:~: metainfo-filename-cid-mismatch
Cockpit renamed its ID to "org.cockpit_project.cockpit" to conform to
the AppStream spec [1]. Follow suit and also fix our own IDs to not
contain hyphens.
[1] 4a9ffe669cCloses#204