OAuth refactor: wire up cdt_identity URLs

[thekaveman]

Currently

• benefits.oauth defines a URLConf
• The top-level benefits.urls URLConf includes the benefits.oauth URLConf under the prefix oauth/

Refactor

• cdt_identity defines a URLConf
• benefits should simply register the routes from cdt_identity

Acceptance criteria

• Routes from cdt_identity.urls are included in the top-level benefits.urls under the prefix oauth/
• The custom hooks defined earlier are injected into the views at this stage
• Any middleware wrappers needed for individual view functions in cdt_identity are applied at this stage