Share url view

* adds modal for rendering the share url
* adds new custom_widget text-to-clipboard-input.html
  * provides a copy button for writing the text input's value into the client's clipboard
* adds translation

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

@@ -1,5 +0,0 @@
-{% 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 %}