Statistics: use secure endpoint

Prevent graph from being blocked because of mixed content.
https://developer.mozilla.org/en-US/docs/Web/Security/Mixed_content?utm_campaign=default&utm_medium=firefox-console-errors&utm_source=mozilla

Remove leftovers from previously supported PHP-version

Use PHPUnit\Framework\TestCase instead of PHPUnit_Framework_TestCase

Refactoring tests

Changes to the translation system made all authX509 messages show
as "Not translated", because the new mapping of error codes to
error messages was not passed to the template.

Doing so allows us to mock the class. Otherwise, the _autoload_module.php is always called first, and when it tries to register the functions from that class, it automatically autoloads it, making it impossible to mock it afterwards.

The OPENLDAP option uses hardcoded uid to search for. It should instead use the value of
attribute.username. This means it also changes the default since attribute.username
defaults to samAccountName. So update the docs to make the example work again. Has not
been in a release yet so should not break existing installations.

(UID was interpreted as HTML tag)

Docs: fix typo's

This prevents a lot of -dev dependencies in composer.lock which are
not used otherwise and generate 'scary' warnings like "Package x is
abandoned".

Closes #718

Fix duplicate assertion error using Redis Store

Added tests for SimpleSAML\XML\Validator

Added php-cs-fixer config

Merge branch 'deprecate-assert-with-string' of https://github.com/fentie/simplesamlphp into PR/fentie-deprecate-assert-with-string and fix conflicts.

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

PSR-2 compliance in lib/SimpleSAML/Auth/ directory

Working toward some of the requested tasks in
https://github.com/simplesamlphp/simplesamlphp/wiki/List-of-tasks

Fix typo in docs/simplesamlphp-sp.md

Might not be complete, needs check with current G Suite interfaces.
But improves on the current situation.