Make order customer email links consistent

Previously the order table would show user account links for
users who had accounts, and mailto links for those who did not.
This inconsistent link behavior is replaced with plaintext for
users who do not have accounts.

backend/app/views/spree/admin/orders/index.html.erb

@@ -184,8 +184,9 @@
           <% if order.user %>
             <%= link_to order.email, edit_admin_user_path(order.user) %>
           <% else %>
-            <%= mail_to order.email %>
+            <%= order.email %>
           <% end %>
+          <%= link_to_with_icon('email', t('spree.actions.send_email'), "mailto:#{order.email}", no_text: true) %>
         </td>
         <td class="align-right"><%= order.display_total.to_html %></td>
         <td class='actions align-center' data-hook="admin_orders_index_row_actions">

core/config/locales/en.yml

@@ -793,6 +793,7 @@ en:
       refund: Refund
       remove: Remove
       save: Save
+      send_email: Send Email
       ship: Ship
       split: Split
       update: Update