Uglify JS & CSS

- Using [grunt-ng-annotate](https://www.npmjs.org/package/grunt-ng-annotate) to deal with Angular injection for by adding notations ready to minify code
- Using [grunt-contrib-uglify](https://github.com/gruntjs/grunt-contrib-uglify) in order to minify the JS files
- Add a task for ``grunt-sass`` in the Gruntfile to compress the CSS files