Enable mwext-VisualEditor-npm, disable -jslint, -csslint

This will run Grunt which, for VisualEditor, will run:
* jshint
* csslint
* node-jscs (NEW)
* standalone qunit (NEW)

Keeping the Jenkins variant of jshint for the 'check' pipeline
since Grunt requires code execution.

Change-Id: Ib05ad8d180d5239ac0b929ee95a9441f8289bbbc