Create the APIs so the frontend can interact with saved views. We'll need support for: * Querying saved views, with filters for `subscribed` as well as for listing all the saved views available in a namespace * Updating a saved view * Deleting a saved view * Subscribing / Unsubscribing from a saved view (i.e. adding / removing a saved view to the nav for a particular user) * Reordering a saved view in the nav for a specific user