Alphabetised the locales list in the treeview

Single-line edit to alphabetise the locales list by [IETF tag](https://en.wikipedia.org/wiki/IETF_language_tag) (so by [ISO 639-1 α2 code](https://en.wikipedia.org/wiki/ISO_639-1)), to make the list easier to read.

It would be better to sort these by [Culture name](http://msdn.microsoft.com/en-gb/library/ee825488(v=cs.20).aspx), but that wouldn't be a single-line edit, so would introduce a [slightly] greater overhead. Also, the table `umbracoLanguage` is already indexed on the column `languageISOCode`, so the overhead of this edit on the SQL server should be minimal.