Consistent naming for organisations, addons, apps.

[divarvel]

Before

clever create -o <org_id> <app_name>
clever link <org_id>/<app_name>
clever addon link <addon_id>

After

clever create [-o (<org_id>|<org_name)] <app_name>
clever link [-o (<org_id>|<org_name>)] (<app_id>|<app_name>)
clever service link-addon (<addon_id>|<addon_name>)
clever service link-app (<app_id>|<app_name>)

That would fix #51.
The clever service stuff will happen in #55