Converting preload to events

Preloads are an event handling system, but limited by both a misleading name, and the inability to dynamically register a new event listener. This change takes care of both issues. Full backward compatibility is mantained for now.

Xoops\Core\Events takes over for XoopsPreload
Xoops\Core\PreloadItem takes over for XoopsPreloadItem
Xoops::getInstance()->events() takes over for ->preload()

modules/(name)/preloads/*.php processing is unchaged (that is the 'preload' part.)
New  method addListener('event.name',callable) to register listeners on the fly
Fix monolog/preloads/core.php error - undefined var $configs