remove vendorCss configuration and its usage in tests + public index.htm...

assets/vendor.css(and the concat task that created it) is not needed anymore by default due to @rjackson pulling qunit via bower(the only code to use it). 

AKA, before this, tests/index.html was loading the css for qunit twice(/vendor/qunit/qunit/qunit.css & assets/vendor.css) and furthermore, public/index.html was loading qunit css once(which never made sense anyway).