Implemented EZP-19411: Avoid file_exists and include calls for register...

...ing datatypes and workflows

See https://github.com/ezsystems/ezpublish-legacy/commit/a6bfaa622342b728951c7f45bb066828440c3be3

Btw, datatype class had no closing php tag in this extension, as probably all the other has... it shouldn't be a problem. let me know if you prefer that i add it in a different commit as CS change