browse: Add a button to navigate to origin url in origin context views

swh/web/templates/includes/origin-visit-snapshot.html

 <div class="panel panel-default" style="overflow-x: auto;">
   <div class="panel-heading">
+    {% if origin_context.origin_info.url|slice:"0:4" == "http" %}
+      <div class="pull-right">
+        <a href="{{ origin_context.origin_info.url }}" class="btn btn-md btn-swh" role="button">Go to origin</a>
+      </div>
+    {% endif %}
     <a href="{{ origin_context.origin_browse_url }}" style="outline:none;">
       <h2 style="text-align: center">SWH origin: {{ origin_context.origin_info.url }}</h2>
+      <div class="clearfix"></div>
     </a>
   </div>
   <div class="swh-origin-visit-details">

swh/web/templates/origin.html

@@ -6,6 +6,11 @@
 
 <div class="panel panel-default" style="overflow-x: auto;">
     <div class="panel-heading">
+      {% if origin_info.url|slice:"0:4" == "http" %}
+        <div class="pull-right">
+          <a href="{{ origin_info.url }}" class="btn btn-md btn-swh" role="button">Go to origin</a>
+        </div>
+      {% endif %}
       <a data-toggle="collapse" data-parent="#accordion" href="#swh-origin-top-collapse" style="outline:none;">
         <h2 style="text-align: center">SWH origin: {{ origin_info.url }}</h2>
         <div class="clearfix"></div>