Issue #2888723 by fenstrat, Petr Illek, kim.pepper, johnennew, Wim Leers, alexpott: ckeditor_stylesheets cache busting: use system.css_js_query_string

Issue #2567861 by Antti J. Salminen, ZeiP, madhavvyas, kekkis, johnennew, boaloysius, Yogesh Pawar, Munavijayalakshmi, chx, alexpott: Add test for enabling modules with incompatible PHP version dependency