This resolves #1009.

We were echoing the result of require(), resulting in a '1' being printed during login

This introduces a "theme.header" configuration option in order to achieve that.

This function can be used to load an asset from a twig template, adding a "tag" parameter to it with a few dynamic bytes depending on the version of SimpleSAMLphp, or the last modification time of the file if we are running master. This behaves as a cache-buster, forcing browsers to reload assets when a new version of SimpleSAMLphp gets installed.

This way we can forget about updating the copyright notice every year.

Create a new "configpage" hook for those modules that need to inject anything in the configuration page.

This allows us to change the signature of the hook, so that we pass it the \SimpleSAML\XHTML\Template object and then the hook can not only add data to be passed to the twig template, but also add its own translation domain. This was needed because many modules were putting their translations inside "core", and when moving those to the modules themselves, the new translation system cannot perform the translation because only the translations for the current module in use are loaded (in the config page, that's the core module). Therefore, we needed a way to get the Localization instance from the template, and a way to pass that to the hook so that the hook can register the translations for its own module.

Twig will always use gettext, legacy will use legacy. Twig does not
work with legacy so new ui would break if you would not also set this
option. Instead, just switch the system in use based on the usenewui
config variable.

This is because some templates, e.g. errror, expect to be able to
include them. This fixes e.g. the No State error page.

This is useful when testing.

*    Updated the phpDoc comments to match the code
*    Added return statements
*    Added return values

This introduces the following:

- The use of Request objects to handle request data to controllers.
- The use of Response objects to model responses that should be sent to the browser.
- The use of "controllers" that are responsible for translating a request into a response.
- The possibility to define your own URLs on each module by specifying them, together with their controllers, in a "routes.yaml" file in the root of a module.
- The new UI is completely separated from the old, so "usenewui" must be set to "true" in the configuration.
- Twigified templates are not used unless we're using the new UI, or the twig template is part of a theme.

This seemed the logical place to do it, because it's essentially
a presentation thing (so in Template, not Locale). There's likely
something to be said for sorting by key aswell as sorting by
translated language name. Picked key for now, seems most predictable.

setupTwigTemplatepaths() cannot return false

This seemed the logical place to do it, because it's essentially
a presentation thing (so in Template, not Locale). There's likely
something to be said for sorting by key aswell as sorting by
translated language name. Picked key for now, seems most predictable.

This allows us to load templates from modules inside a twig template itself (include, embed, etc), even when the main template is not in a module or in a different one.

This can be used by templates to load resources in different ways, either optimized for the developer or for a production environment.

This allows us to use this new filter to translate strings from a given array of translations, where every translation is indexed by its ISO 639 code. A new configuration option ('language' -> 'priorities') is available too to control the alternative languages that can be used instead of a given language, when the latter is not found. The filter returns null when no suitable translation is found, so that it can be combined with "default()" to set a default translation for a given string.

This resolves #695.