self-registration with redirect not working

[loomis]

The self-registration is not working because of:

• The UI hint fields in the user template resources are not stripped before trying to create the user record.
• When a redirect is specified, the user creation for the self-registration method is completely ignored.

Fix both problems and expand the tests to ensure that these failure cases are covered.

[loomis]

For information, this fix is deployed on Nuvla.

[mebster]

Works on Nuvla indeed.

Things to improve:

• the response of the validation link (e.g. https://nuv.la/api/callback/4431e0e2-50d1-4e6a-8d89-ba0418330328/execute) returns an application/json type instead of pretty html. A more convenient response would include a welcome message and a way to login. (provide better browser workflow for callbacks #1628)
• the validation email should be a bit more informative and include more clearly the source of the request (e.g. Nuvla) (make email validation email more informative #1627)
• T&C approval is missing (terms and conditions agreement #1579)

[loomis]

I've added issues for those items.