Issue #2457781 by prateekMehta, stefan.r, AjitS, hussainweb: Use Utility\Html class instead of Utility\String for decodeEntities() function

Issue #2457887 by prateekMehta, stefan.r, rpayanm, alexpott: Use Utility\SafeMarkup class instead of Utility\String for placeholder(), checkPlain(),format() functions

Issue #2427095 by likin, idebr, prateekMehta: Formatting guidelines are not shown for textareas without WYSIWYG