Copy docs to older/4.0/

schleuder/docs/older/4.0/_list_usage_basics.md

schleuder/docs/older/4.0/changes.md

schleuder/docs/older/4.0/concept.md

schleuder/docs/older/4.0/index.md

schleuder/docs/older/4.0/list-admins.md

schleuder/docs/older/4.0/projects-and-plugins.md

schleuder/docs/older/4.0/providers.md

schleuder/docs/older/4.0/schleuder-schema-resend-small.png

schleuder/docs/older/4.0/schleuder-schema-resend.png

schleuder/docs/older/4.0/server-admins.md

schleuder/docs/older/4.0/subscribers.md