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
* Move notification texts to a slightly different layer (#4572)
* Further Simplify/refactor the actions/notification layer (#4573)
1. Move the 'with-feedback' actions to a 'with-blocking-action' mixin
which better describes what it does
2. Additional set of unit tests almost over the entire layer to prove
things work/add confidence for further changes
The multiple 'with-action' mixins used for every 'index/edit' combo are
now reduced down to only contain the functionality related to their
specific routes, i.e. where to redirect.
The actual functionality to block and carry out the action and then
notify are 'almost' split out so that their respective classes/objects do
one thing and one thing 'well'.
Mixins are chosen for the moment as the decoration approach used by
mixins feels better than multiple levels of inheritence, but I would
like to take this fuether in the future to a 'compositional' based
approach.
There is still possible further work to be done here, but I'm a lot
happier now this is reduced down into separate parts.
John Cowen