Add warning message to enterprise ship methods list and ship method edit page

app/views/admin/enterprises/form/_shipping_methods.html.haml

@@ -1,4 +1,6 @@
 - if @shipping_methods.count > 0
+  .row
+    = t 'spree.admin.shipping_methods.form.deactivation_warning'
   %table
     %thead
       %tr

app/views/spree/admin/shipping_methods/_form.html.haml

@@ -1,6 +1,8 @@
 = admin_inject_shipping_method
 .alpha.eleven.columns{ "ng-app" => "admin.shippingMethods",
   "ng-controller" => "shippingMethodCtrl" }
+  .row
+    = t '.deactivation_warning'
   .row
     .alpha.three.columns
       = f.label :name, t(:name)

config/locales/en.yml

@@ -3246,6 +3246,7 @@ See the %{link} to find out more about %{sitename}'s features and to start using
           zones: "Zones"
           both: "Both Checkout and Back office"
           back_end: "Back office only"
+          deactivation_warning: "De-activating a shipping method can make the shipping method disappear from your list. Alternatively, you can hide a shipping method from the checkout page by setting the option 'Display' to 'back office only'."
       payment_methods:
         new:
           new_payment_method: "New Payment Method"