Improve and unify error messages

[edmundoa]

In most of our stores we have user notifications to alert the user when the request to the server failed. We usually show the HTTP response code in the text, but when the server times out we just show an empty string. We should handle this specific case and show a proper error message.

We should also unify the messages in terms of showing names instead of IDs when possible, and not use exclamation marks (alerts are already red and in bold text).

[edmundoa]

I'm moving the part of handling empty errorThrown on XHR responses into 1.1.1.