Enhancement: Prefer 127.0.0.1 as OAuth redirect URL

When using OpenID Connect we now always use http://127.0.0.1
as redirect URL instead of http://localhost, following the recommendations in RFC 8252   (https://tools.ietf.org/html/rfc8252).
For OAuth2 we added a branding parameter which allows to specify http://127.0.0.1 instead
of http://localhost.

https://github.com/owncloud/enterprise/issues/4542
