Switch language also in IE...

This PR enables to switch languages also in IE...

What was done:
* Let Ext manage DOM events
* Response of getLanguage is now json
* a `init_main` function was created. This one is called after the Ext ajax request on get_language has received a response.
* for `set_language`, a random parameter was added in order to be sure that IE fires the request (you should also use Ext here... I leave it up to you)
* Some identation errors were corrected.

Personally, I would prefer that we use the `var toto = function(params){};` syntax instead of `function toto(params){};`, because it is much easier to see if the given variable is a parameter or a function inside a function.

Please DO NOT forget to declare js variables local!! (using `var`), otherwise it soon is going to be a big mess...

Please review, comments are MANDATORY!!!