refactor file drop widget

src/Bundle/ChillMainBundle/Resources/views/Form/fields.html.twig

@@ -162,6 +162,7 @@
 {% block chill_collection_widget %}
     <div class="chill-collection">
         <ul class="list-entry"
+            {{ form.vars.js_caller }}="{{ form.vars.js_caller }}"
             data-collection-name="{{ form.vars.name|escape('html_attr') }}"
             data-collection-identifier="{{ form.vars.identifier|escape('html_attr') }}"
             data-collection-button-remove-label="{{ form.vars.button_remove_label|trans|e }}"
@@ -173,7 +174,7 @@
                         {{ form_widget(entry) }}
                         {{ form_errors(entry) }}
                     </div>
-                </li> 
+                </li>
             {% else %}
                 <li data-collection-empty-explain="1">
                     <span class="chill-no-data-statement">{{ form.vars.empty_collection_explain|default('No entities')|trans }}</span>