Have Grunt render a ie8 css file

This is the stripmq grunt task that will create a separate moodle-ie8.css file. With this font locations and pix using [[theme:pix|pixname]] are broken for IE8. Perhaps that can be fixed with grunt too. (I need to look into regex using grunt combining them with $CFG->wwwroot values. 

As for the include in default.php I am not sure this will work on all occasions.
@ds125v please review as this is my first pull request on my own repo and my first attempt at writing Grunt stuff.