Add language download feature

[ywarnier]

This is a little more of a long shot, but we should have a chash feature that allows us to download the latest version of a language package from Github, or http://i18n.chamilo.org. Not sure how this should be structured in Github but on the Chamilo server this could just be an image of the github repo, which synchronizes and zips each language directory every hour or so.
The files should contain a little manifest explaining what language is contained in the directory and how it should be inserted (parent language directory name, language name, directory, version and ISO code).