Changed editor error management to new error system

Closes #862
A reference to "this" points to the options you handed over to the ajax function (the url, data, successFn, errorFn object). Is this intended?
If I see this correctly, simply calling "new errorWindow({error:error});" should be enough here as there is no need to control this errorWindow from anywhere else except inside the errorWindow itself.
(this comment applies to all these kinds of changes)