"core" needs to be able to wrap some content in tabs

Replaces the need for `$this->data['htmlinject']`

Note that the flag in the context must be named 'clipboard',
not 'clipboard.js'. This is because the dot is an illegal symbol in
variable names in twig.

This module is hereby twigified. For #499.

Fixed incorrect memcache_store prefix docs.

Add "config-templates", "metadata-templates" and "templates" to the list of directories where we look for PHP files to check their syntax.

Fix object operator bug on templates/metadata.php

Fix a cosmetic exception when using loginuserpassorg.php

When using ldap:LDAPMulti, SimpleSAMLphp generates an exception:

 SimpleSAML_Error_Exception: Error 8 - Undefined index: rememberMeEnabled
 Backtrace:
 4 /srv/simplesamlphp-1.14.8/www/_include.php:83 (SimpleSAML_error_handler)
 3 /srv/simplesamlphp-1.14.8/modules/core/templates/loginuserpass.php:107 (require)
 2 /srv/simplesamlphp-1.14.8/lib/SimpleSAML/XHTML/Template.php:577 (SimpleSAML_XHTML_Template::show)
 1 /srv/simplesamlphp-1.14.8/modules/core/www/loginuserpassorg.php:95 (require)
 0 /srv/simplesamlphp-1.14.8/www/module.php:137 (N/A)

This is because the loginuserpass.php template (which is used by both
loginuserpass.php and loginuserpassorg.php) refers to
$this->data['rememberMeEnabled'], but that variable is only defined when
you make use of loginuserpass.php.

Since these don't appear to be relevant to loginuserpassorg.php, this
patch simply sets these to false (the default value), so that they're
no longer undefined.

Fix OID error, 1.2.752.194.10.4 should be 1.2.752.194.10.2.4

Add a couple of methods to perform translations with PHP's native gettext implementation, and start using them.

Add also proofs of concept for every example given.

Since the class names were prepended with "\", the original extension was used, instead of our own wrapper. This fixes that issue, and sets the two new methods in SimpleSAML\Locale\Translate as the functions to use to replace the calls to gettext() and ngettext(). Support for the old translation system is still missing for twig templates.

Define SimpleSAML\XHTML\Template::$twig as a property (previously only set in the constructor) and make sure we use proper type checking when using it.