Added shim support

This PR adds shim support to this bundle.

bower.json
```
{
  "name": "Project name",
    "version": "1.0.0",

    "dependencies": {
        "angular": "latest",
        "jquery": "latest",
        "requirejs": "latest"
    }
}
```

.bowerrc
```json
{
    "directory" : "src/Acme/ProjectBundle/Resources/public/components"
}
```

base.html.twig
```twig
{% block javascripts %}
    {% javascripts filter='?requirejs' '@AcmeProjectBundle/Resources/public/js/apps/dashboard.js' %}
        {{ require_js_initialize({ 'main' : asset_url }) }}
    {% endjavascripts %}
{% endblock %}
```

requirejs.yml
```yml
hearsay_require_js:
    paths:
        angular: @AcmeProjectBundle/Resources/public/components/angular/angular
        jquery:  @AcmeProjectBundle/Resources/public/components/jquery/jquery

    shim:
        -
            name: angular
            deps: [jquery]
            exports: angular
```

dashboard.js
```javascript
require(['angular'], function(angular) {
    console.log(angular);
});
```