LB-1523 Remove Backbone, jQuery and underscore from global scope

Take advantage of the use-amd plugin to allow loading of Backbone, jQuery and underscore (and other libraries with support for noConflict mode), without adding them to the global scope.

[use-amd](https://github.com/tbranyen/use-amd) implements a functionality similar to require.js ```shim```, but ```shim``` doesn't allow libraries to be loaded in noConflict mode (see https://groups.google.com/forum/#!topic/requirejs/vmRntf_d7ok).

Plugin usage:
* Add libraries to use configuration inside require.js in noConflict mode:
```javascript
use: {
      jquery: {
           attach: function() {
               return $.noConflict();
           }
      }
}
```
* Require the libraries using the plugin:
```javascript
require(['use!jquery'], function($) {
    // do something that requires jQuery, it won't be added as a global
});
```