Support for Javascript-based Language Cookie redirect

This module is often used alongside the Language Cookie module in order to remember the language choice on the language selection page.

When using a page cache such as varnish (and thus not running any PHP), we cannot implement any cookie-based redirect logic in PHP so we may want to do this in Javascript insteda

The attached patch adds a setting to enable automatic Javascript-based redirects based on the language stored in the language cookie so that the redirect also works on cached pages.