MDL-42151 import YUI 3.13.0 and switch to emulated SimpleYUI

Includes @version@ fix
MDL-42152 AJAX: Add rollup support to YUI loader
MDL-42152 Use new rollup system
MDL-42152 improve SimpleYUI docs
MDL-42152 rename our rollup to start with 'yui-' to enable the stadnard regex base magic
MDL-42152 add more YUI rollup explanation from Andrew
MDL-42223 JavaScript: Deprecate $CFG->cachejs in favour of $CFG->debug