Raise errors in development mode on deprecation

We've had quite some time to find the deprecation errors in Ember and
most should be fixed. It is time to turn up the difficulty, which will
raise exceptions in development/test mode if a deprecation is present.
This will force developers to fix them as they encounter them.

app/views/common/_discourse_javascript.html.erb

@@ -24,6 +24,12 @@
     <% end %>
     window.onerror(e && e.message, null,null,null,e);
   });
+
+<% if Rails.env.development? || Rails.env.test? %>
+  Ember.ENV.RAISE_ON_DEPRECATION = true
+  Ember.LOG_STACKTRACE_ON_DEPRECATION = true
+<% end %>
+
 </script>
 
 <script>