Ref #933 - dev and build tasks for Grunt

Dev: don't minify
Build: minify, lean Modernizr build

Dev assets will load if you have defined your WP_ENV as development
If you don't use Bedrock, you'll need to add this to your wp-config.php:

define('WP_ENV', 'development');

TODO: lib/scripts.php shouldn't need to be committed for changes after
running the version task

package.json

@@ -27,6 +27,7 @@
     "grunt": "~0.4.2",
     "grunt-contrib-clean": "~0.5.0",
     "grunt-contrib-jshint": "~0.6.4",
+    "grunt-contrib-concat": "~0.3.0",
     "grunt-contrib-uglify": "~0.2.4",
     "grunt-contrib-watch": "~0.5.3",
     "grunt-contrib-less": "~0.8.1",