Update to use grunt 0.4.x

Change directives code to grunt template syntax. Register new grunt modules
as tasks. Update default and minify task to use updated tasks. Add grunt
modules to package.json.

Remember to switch from grunt 0.3 to grunt 0.4 use:
$ npm uninstall -g grunt
$ npm install -g grunt-cli
$ npm install # from webinos dir to install new grunt deps

Jira-issue: WP-779