Route models root should be created at the root

Currently, the route models root is created below the first container of type domain it finds. Consequence: if DAM is deployed, it is created under the assets folder, and no workflow appear on the start workflow widget.

We should have a root container for route models, and the query that fills the start route widget should query both on that root container and in the current domain (for future compability with multi-tenancy use cases)