Adds current language code for django-cms plugin editor

Hello, 
This issue has some history:
I made a  pull request 4 months ago, including a input tag for making django-cms be able to get current language: cf4be068f5

You stated that would be better to include a tittle into the span, as a better solution to having a hidden <input> element.

But this other solutions needs django-cms js plugin to  be changed.

Just now i have seen a pull request which does the same:
Related to #69

This patch adds the title field to current span, and I have a django-cms pull request ready to be sent, which will add suport to get language from current span title  (Also fixes another django-cms issue for language).

Maybe we should apply both solutions: the #69 for old django-cms instances to work, and this current span titlte for doing things well :).