Add logoff button for admin-interface

This means we can remove the crystal_project icons when removing
the old templates.

Closes: #952

There's some redundancy now since the code must support the old
and new template. The links variety is not very beautiful, but the
old one wasn't either..

Also search for "en" as a final fallback language to find a displayable
name should such a name not be found in the current language and the
default language.

When we remove old templates we can also remove silk.

The former is no longer online.

There's a link straight above to the docs, a link to the rest
of the website in the footer, this paragraph is highly redundant.
It links to rnd.feide.no which is down.

This is likely way more informative for the average person
clicking the link - and linking directly to github only
stimulates people asking help questions in issue tracker.

Fix new UI

Do not enable complementary functionality by default

In the ldap-code, search.attributes can be either a string (single attribute) or an array of attributes... The negotiate attr-setting is equal to search.attributes, but was handled differently (as merely a string)

PasswordProtectedTransport authncontext when HTTPS

Add docs for saml:AuthnContextClassRef filter

Following up on the idea mentioned in #937: If the transport is secure fall back to the `PasswordProtectedTransport` authn context class ref, otherwise keep the current default of `Password`.

Requires a version of the SAML2 library with simplesamlphp/saml2#129 merged due to the reference on a newly defined Constant.

Fix for #933