Previously, would show inappropriate precision, like "0.0598134 hours ago"
or "1490532.4129 hours from now" depending on the expiration date.

(cherry picked from commit 1bc5ae80)

* 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

* Added Kernel class to handle request

* Kernel handle request

Kernel is loaded in SimpleSAML\Module class
Removed Router and ControllerResolver classes

* Added route command (squash)

* Use symfony application and cache

* Updated to today's standards

* Fix for Symfony4 & Catch environment from ENV variable

* Standardize location of routes/services files

* Trying to make slashes work properly in all situations

* Convert XML to YML

* Fix some template-names and endpoints

* Rename Controller-classes

* Update dependencies

* Fix routing files

* TooManyArguments

* Fix TypeCoercion

* PSR-12

* Fix rebase mistake

* Rebase lock-file

* Fix Psalm

* Add strict_types declaration

Co-authored-by: Sergio Gómez <decano@gmail.com>

* Raise minimum PHP version to 7.0

* Remove tests pre-PHP 7.2

* Upgrade dev dependencies

* Ignore tests for deprecated class

* Add typehints; not touching public API

* Remove none-array replacements-param; old behaviour from pre-1.4 release

* Psalm fixes

* Add upgrade notes

* PSR-12

PSR-12 compliancy

This ensures that we don't break any existing modules by renaming a template from ".php" to ".tpl.php".

The old mail class uses the built-in `mail` function in PHP, and builds a payload by itself using hard-coded HTML and MIME-snippets. Let's use a library for that; PHPMailer has new dependencies and does all the heavy lifting.

re-add it and fix all templates that depended on it being unset

class_implements() returns class names without leading backslash

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.