Normalize LDAP user DNs (downcase and remove excess spaces)

See merge request gitlab-org/gitlab-ce!14697

Remove old navigation CSS

See merge request gitlab-org/gitlab-ce!14573

I first attempted to extract logic from the code that normalizes DNs, but I was unsuccessful. This is a hack but it works.

Since that behavior changed, and is now under the malformed DN context.

Especially from the last attribute value.

Disabling some for now since this is based on `Net::LDAP::DN`.

for normalizing and parsing DNs