Document upload

* adds document upload form
* refactors modal form templates into form classes
* adds document upload route to intervention routes of urls.py

intervention/templates/intervention/detail/related-documents.html

@@ -12,12 +12,10 @@
                         </div>
                         <div class="col-sm-6">
                             <div class="d-flex justify-content-end">
-                                <a href="{% url 'doc-new' %}" title="{% trans 'Add new document' %}">
-                                    <button class="btn btn-outline-default ">
-                                        {% fa5_icon 'plus' %}
-                                        {% fa5_icon 'file' %}
-                                    </button>
-                                </a>
+                                <button class="btn btn-outline-default btn-modal" data-form-url="{% url 'intervention:new-doc' intervention.id %}" title="{% trans 'Add new document' %}">
+                                    {% fa5_icon 'plus' %}
+                                    {% fa5_icon 'file' %}
+                                </button>
                             </div>
                         </div>
                     </div>