Closes: #1604

updated twig to version 3 and added wrapper for translation via symfony/twig-bridge

Co-authored-by: Ulrik nielsen <un@ipwsystems.dk>

- Fix not working rememberchecked config option
- Tweak layout a bit
- Improve display when there are no IdPs configured/found

These pages are now handled by the admin module. Add redirects
to the new locations.

post.* has been added directly under assets for now, tried it
via webpack but this added a several times overhead to these
very small files, so this seemed the cleanest solution for now.
But might be improved upon.

In the modern template also clean up HTML a bit.

* Use strict variables in Twig, except for our TemplateTest; throw exception on missing variables

* Fix issues due to Twig strict_variables=true

* Fix for #1229

* Fix metadata-template

This can be removed in 2.0 when we drop the old templating system.

If there is no "general" block defined in the expander, it just won't show.

This was inline in the script, and later migrated to a twig template. This made us force the use of twig, or otherwise the template would not work for the old user interface. We shouldn't do that, and we should have a proper PHP template in place.

Old PHP templates are going to disappear anyway, so let's not break anything for a change that will be removed in the near future. We keep the .tpl.php extension though.

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.

- Make textarea and code-box monospace (might be subjective)
- Jump to converted data after form submit
- Make file upload label work

Closes: #1094