Make error codes easier to extend (#1870)

* 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>