Adapt images tree to work with several ogServers

Images view fetch images from all ogServers configured and show them in
the left tree as a nested list. ogServers are represented as the parents
of their images.

ogcp/templates/images.html

@@ -11,14 +11,20 @@
 {% endblock %}
 
 {% block sidebar %}
-    <ul id="images" class="nav flex-column nav-pills">
-        {% for image in images %}
-            <li id="{{ image["name"] }}_{{ image["id"] }}" class="nav-item">
-                <input class="form-check-input" type="checkbox" form="imagesForm"
-                       value="{{ image["id"] }}"
-                       {% if image.get("selected", False) %}checked{% endif %}
-                       name="{{ image["name"] }}_{{ image["id"] }}" />
-                        {{ image["name"] }}
+    <ul id="servers" class="nav flex-column nav-pills">
+        {% for response in responses %}
+        <li class="nav-item"><b>{{ response["server"]["name"] }}</b>
+                <ul id="images" class="nav flex-column nav-pills">
+                    {% for image in response["json"]["images"] %}
+                        <li id="{{ image["name"] }}_{{ image["id"] }}" class="nav-item">
+                            <input class="form-check-input" type="checkbox" form="imagesForm"
+                                   value="{{ image["id"] }}"
+                                   {% if image.get("selected", False) %}checked{% endif %}
+                                   name="{{ image["name"] }}_{{ image["id"] }}" />
+                                    {{ image["name"] }}
+                        </li>
+                    {% endfor %}
+                </ul>
             </li>
         {% endfor %}
     </ul>

ogcp/views.py

@@ -1377,9 +1377,8 @@ def commands():
 @app.route('/images/', methods=['GET'])
 @login_required
 def images():
-    r = g.server.get('/images')
-    images = r.json()['images']
-    return render_template('images.html', images=images)
+    responses = multi_request('get', '/images')
+    return render_template('images.html', responses=responses)
 
 
 @app.route('/repositories/', methods=['GET'])
@@ -1645,10 +1644,10 @@ def action_image_info():
     form.permissions.data = image['permissions']
     form.software_id.data = image['software_id']
 
-    images = g.server.get('/images').json()['images']
+    responses = multi_request('get', '/images')
 
     return render_template('actions/image_details.html', form=form,
-                           images=images)
+                           responses=responses)
 
 @app.route('/action/image/delete', methods=['GET', 'POST'])
 @login_required
@@ -1671,14 +1670,14 @@ def action_image_delete():
         if not validate_elements(images, max_len=1):
             return redirect(url_for('images'))
         image_name, image_id = images[0]
-        r = g.server.get('/images')
+        responses = multi_request('get', '/images')
         form.ids.data = image_id
         if not validate_elements(images, max_len=1):
             flash(_('Please select one image to delete'), category='error')
             return redirect(url_for('images'))
         return render_template('actions/delete_image.html', form=form,
                                image_name=image_name.split('_', 1)[0], image_id=image_id,
-                               images=r.json()['images'])
+                               responses=responses)
 
 @app.route('/action/log', methods=['GET'])
 @login_required