New admin page for invitations

app/views/admin/invitations/index.html.erb

@@ -0,0 +1,25 @@
+<section>
+  <h2>Invitations</h2>
+
+  <% if @invitations_used.any? %>
+    <h3>Accepted (<%= @invitations_used.length %>)</h3>
+    <table>
+      <thead>
+        <tr>
+          <th>Token</th>
+          <th>Accepted</th>
+          <th>Invited user</th>
+        </tr>
+      </thead>
+      <tbody>
+        <% @invitations_used.each do |invitation| %>
+          <tr>
+            <td class="overflow-ellipsis"><%= invitation.token %></td>
+            <td><%= invitation.used_at.strftime("%Y-%m-%d") %></td>
+            <td><%= User.find(invitation.invited_user_id).address %></td>
+          </tr>
+        <% end %>
+      </tbody>
+    </table>
+  <% end %>
+</section>