Adds namespace support to the UI:
1. Namespace CRUD/management
2. Show Namespace in relevant areas (intentions, upstreams)
3. Main navigation bar improvements
4. Logic/integration to interact with a new `internal/acl/authorize` endpoint
1. Check the dc's model for both dcs list and the requested dc.
2. If the dc model doesn't exist use and empty array for dcs and a fake
dc with the Name 'Error' as we can't even trust what is in the
`paramsFor`