Fix ArtifactResolution due to misuse of Issuer

Convert to our wrapper class for assertions

Few small improvements

Check explicitly whether array element is defined

Check whether http://macedir.org/entity-category is set in the EntityAttributes
before using it as argument in in_array(). This prevents a "TypeError:
in_array() expects parameter 2 to be array, null given" error.

This situation happens when we do have EntityAttributes in the metadata but
none of type "http://macedir.org/entity-category". An example is an IdP
supporting https://refeds.org/category/research-and-scholarship, which would
have "http://macedir.org/entity-category-support" but not per se also
"http://macedir.org/entity-category".

We can remove several tags, login:processing and admin:metaconv_selectfile, and
replace several others with their English text.

It's easiest prevented by adding a linebreak after the <code> tag. This is not
ideal but a quick fix.

Fixes 336b7abe which changed the label from
'Login' to a single-use 'Log in' whilste the translations only have 'Login'.

* locales/de: Fix several wording, typo and grammar mistakes

* Fix typo

Co-authored-by: Tim van Dijen <tvdijen@gmail.com>

An issue in the code prevented the SameSite session cookie option from being set the first time we were reaching SSP when using PHP versions older than 7.3.

This fixes #1320

* fixed warning when Warning: session_create_id(): Failed to create new ID in /var/ssosp/lib/SimpleSAML/SessionHandlerPHP.php

* Use session_create_id() unconditionally

In master, we require PHP 7.2, which is guaranteed to provide `session_create_id()`. Therefore, we don't need the if clause any longer. Add also a warning when `session_create_id()` fails, and fall back gracefully to our old way to create session IDs.

Co-authored-by: Jaime Pérez Crespo <jaime.perez@uninett.no>