FEATURE: further restrict downloading of backups

- send email to logged in admin when they press the "download" button
- show pop-up that email was sent
- create email template
- require a valid token to download backup

app/views/admin/backups/show.html.erb

@@ -0,0 +1,7 @@
+<div id="simple-container">
+  <%if @error%>
+    <div class='alert alert-error'>
+      <%= @error %>
+    </div>
+  <%end%>
+</div>