Locales improvement

* A preview of the base frontend URL of a locale is now present in the locale edit form.
* Locale ordering is now taken into account in many backend queries related to the locale.
* Language dropdown in the locale edit form has been improved and grouped.

![screenshot_2013-11-19_2_24_pm](https://f.cloud.github.com/assets/874403/1575608/43e24d2e-5150-11e3-9770-e72560907f28.png)