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

konova/templates/konova/custom_widgets/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 %}

konova/templates/konova/custom_widgets/text-to-clipboard-input.html

@@ -0,0 +1,18 @@
+{% load i18n fontawesome_5 %}
+
+<div class="input-group" title="{{ widget.value|stringformat:'s' }}">
+    <input aria-describedby="copy-btn" type="{{ widget.type }}" name="{{ widget.name }}"{% if widget.value != None %} value="{{ widget.value|stringformat:'s' }}"{% endif %}{% include "django/forms/widgets/attrs.html" %}>
+    <div class="input-group-append" onclick="copyClipboard()">
+        <span id="copy-btn" class="btn btn-default" value="{% trans 'Copy to clipboard' %}" title="{% trans 'Copy to clipboard' %}">{% fa5_icon 'clipboard' 'far' %}</span>
+    </div>
+</div>
+
+<script>
+    function copyClipboard() {
+      var copyText = document.getElementById("id_{{ widget.name }}");
+      copyText.select();
+      copyText.setSelectionRange(0, 99999); /* For mobile devices */
+      document.execCommand("copy");
+      alert("{% trans 'Copied to clipboard' %}");
+    }
+</script>