core.js should be loaded directly after jQuery and after every other JS file

The file core.js sets up most of the AJAX and jQuery related framework for phpBB. Due to this, it needs to be included right after jQuery has been included. Currently, it is however loaded with INCLUDEJS which causes it to be loaded after every other javascript file except for the style specific ajax.js. This causes every javascript file that is included before core.js and that is using the phpBB AJAX functions or variables to break.