Allow themes to inherit module templates

Migrate logout to twig

It doesn't make much sense anyway. Makes the original templates harder to format, and browser developer tools can provide hierarchical indentation anyway. This allows us to save quite a few bytes per page, write cleaner templates, and forget about how it would look like in the resulting HTML.

This is no longer required in HTML 5.

Non-JS version still needs work. We need to review also non-iframe logout.

This allows us to get rid of inline styles.

Make it a bit better for those with javascript disabled, and add a CSP.

Fixes psalm error.

Show expired entities in federation-page

The template is already able to handle expired entities