build and render secured URL to invite admin

For clarity and a better understanding, use a dedicated controller to
build and render the confirmation URL to share in order to add a new
administrateur.

app/views/manager/application/_navigation.html.erb

@@ -12,7 +12,7 @@ as defined by the routes in the `admin/` namespace
 
   <hr />
 
-  <% Administrate::Namespace.new(namespace).resources.each do |resource| %>
+  <% Administrate::Namespace.new(namespace).resources.select { |resource| resource.to_s != "confirmation_urls" }.each do |resource| %>
 
     <%= link_to(
       display_resource_name(resource),

app/views/manager/confirmation_urls/new.html.erb

@@ -0,0 +1,22 @@
+<% content_for(:title) { "Ajout d'un administrateur" } %>
+
+<header class="main-content__header" role="banner">
+  <h1 class="main-content__page-title">
+    <%= content_for(:title) %>
+  </h1>
+</header>
+
+<section class="main-content__body">
+  <p>
+    Veuillez partager ce lien avec un autre super admin pour que l'opération soit effectuée.
+  </p>
+  <dl>
+    <dt class="attribute-label">
+      Lien
+    </dt>
+    
+    <dd class="attribute-data">
+      <%= @url %>
+    </dd>
+  </dl>
+</section>