Callback routes

[regilero]

• Introduce OIDCHelper, as trying to manipulate routes directly from the provider would make infinite dependencies loops with settings.
• get_urlpatterns is moved inside OIDCHelper
• Side note: when using get_urlpatterns to generates routes in tests this must be defined in the test settings and cannotbe overriden later in individual tests, as the route assignement is done early
• Fix the callback_uri_name/callback_path/callback names mess tobe able to handle routes with prefix. e2e tests done in lemonldap integration currently.

[gbip]

Ici je pense qu'il faudrait résoudre le nom de l'url avec la fonction reverse (ou reverse_lazy) de jdango.