Major update to project structure and dependencies.

* Switched from `requirejs` to `browserify` for client-side JavaScript.
* Removed i18n support due to removal of `requirejs` for now.
* Improved Backbone.Marionette code structure and usage.
* Improved socket.io auto-retry logic.
* Updated `bootstrap` to version 3.
* Switched from `sass` to `less` for CSS preprocessing.
* CSS and JS files are shared between server and client.
* Server renders `client/404.html` for 404 errors.
* Updated all bower and npm modules up to date.
* Grunt task name renamed from `grunt server` to `grunt` and `grunt` to `grunt build`.