Template improvements

* refactors templates/table.html into templates/generic_index.html
* adds DummyFilterInput as do-not-render-widget
* hardens combination of q filter and other filters on index view rendering

intervention/templates/intervention/dummy-filter-input.html

@@ -0,0 +1,5 @@
+{% comment %}
+    This is an empty template.
+    It's used to dismiss a default widget for a django_filter filter and to use a predefined input directly in the
+    template without losing the comfort of matching the filter methods declared in the filter
+{% endcomment %}