Use proper icon for breadcrumb

Uses the asset from the GOV.UK Frontend Toolkit.

app/assets/stylesheets/components/navigation.scss

@@ -40,6 +40,16 @@
 
   }
 
+  &-breadcrumb {
+    display: inline-block;
+    width: 6px;
+    height: 11px;
+    margin: 0 5px;
+    background-image: file-url("separator-2x.png");
+    background-size: 6px 11px;
+    background-repeat: no-repeat;
+  }
+
   li {
     @include core-19;
     margin: 0;

app/templates/org_template.html

@@ -10,7 +10,7 @@
       <div class="navigation-service-name">
         {% if current_user.platform_admin %}
           <a href="{{ url_for('.organisations') }}">Organisations</a>
-          &gt;
+          <span class="navigation-breadcrumb"></span>
         {% endif %}
         {{ current_org.name }}
       </div>