Fixes #1899

Co-authored-by: Simon Jarrett <simonjarrett@capuk.org>

Only 'admin' is enabled additionally, 'core' and 'saml' are enabled by default in \SimpleSAML\Module::isModuleEnabled().

* Fix static call for non-static method in bin/initMDSPdo.php

* Fix phpcs

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Co-authored-by: Marko Ivančić <marko.ivancic@srce.hr>

* For descriptions, check error code existance in descriptions rather than in titles

* Prepare error code constants

* Propagate error codes through the codebase

* Make error codes more extendable

* Fix spell check errors from CICD

* Fix phpcs errors

* Move from static to instance methods

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Co-authored-by: Marko Ivančić <marko.ivancic@srce.hr>
Co-authored-by: Tim van Dijen <tvdijen@gmail.com>

PHP Warning:  Trying to access array offset on value of type null

* Changed the UNIQUE key to a PRIMARY key for the tableVersion and LogoutStore tables for better compatibility with Drupal.

* Increased version number of 'saml_LogoutStore' table to 5 and initialized version number of 'tableVersion' table to 1; older versions of these tables are updated with PRIMARY KEY replacing UNIQUE.

* Move the custom Error- and Exception handlers to their own classes

Co-authored-by: Guillaume Rousse <guillaume.rousse@renater.fr>