adding confirmation template

For action which require a confirmation message.

This is a way to have a template for every confirmation message in the
app.

Example of usage :

```
    {{ include('ChillMainBundle:Util:confirmation_template.html.twig',
        {
            # a title, not mandatory
            'title'             : 'Remove membership'|trans,
            # a confirmation question, not mandatory
            'confirm_question'  : 'Are you sure you want to remove
membership of "%name%" from the group "%group%"?'|trans({ '%name%' :
person.firstname ~ ' ' ~ person.lastname, '%group%' :
membership.cgroup.name }),
            # a route for "cancel" button (mandatory)
            'cancel_route'      : 'chill_group_membership_by_person',
            # the parameters for 'cancel' route (default to {} )
            'cancel_parameters' : { 'person_id' : membership.person.id
},
            # the form which will send the deletion. This form
            # **must** contains a SubmitType
            'form'              : form
        } ) }}

```

Resources/views/Util/confirmation_template.html.twig

@@ -0,0 +1,22 @@
+{% if title is defined %}
+    <h2>{{ title }}</h2>
+{% endif %}
+
+{% if confirm_question is defined %}
+    <p class="message-confirm">{{ confirm_question }}</p>
+{% endif %}
+
+{{ form_start(form) }}
+
+<ul class="record_actions">
+    <li>
+        <a href="{{ path(cancel_route, cancel_parameters|default( { } ) ) }}" class="sc-button bt-cancel">
+            {{ 'Cancel'|trans }}
+        </a>
+    </li>
+    <li>
+        {{ form_widget(form.submit, { 'attr' : { 'class' : "sc-button bt-delete" } } ) }}
+    </li>
+</ul>
+        
+{{ form_end(form) }}