use the configured attribute as the group name rather than
the DN

* Check responseHeaders presence before use them

And so avoid some messages in log file.

It is deprecated as of PHP 7.2

Metarefresh had an inadvertent dependency on the translation files for
the aggregator module that was removed in v1.15. Remove that dependency
and provide the basis for the rest of the module to be translated.

Change the source attribute to `eduPersonPrincipalName` and add missing commas.

As per mailinglist-discussion, consent-stats were never processed by the statistics-module due to inconsistent logging:
https://groups.google.com/forum/#!topic/simplesamlphp/Gc97OeUox2k

The assignment to $stateID is dead and can be removed.

Notice: Undefined index: libevent in modules/memcacheMonitor/templates/memcachestat.tpl.php on line 60

Per https://developers.facebook.com/docs/facebook-login/security/#strict_mode the
`state` parameter should be used for any state needed after the redirect, and the
redirect URI should remain constant.

This picks up the case where the memberof attribute is an empty
array as well as not being an array

Fixes #656