Possibility to hook i18n when returned value for a key is an object rathern than a string


Possibility to hook i18n when returned value for a key is an object rathern than a string.

(NB: not sure i'm not reinventing the wheel i.e "context" stuff)

Exemple:

* jsonfile

```
{
    "myKey":{
        "FOO":"myFoo",
        "BAR":"myBar"
}
```

* javascript

```
i18n.init({
    objectKeyHandler : function(ns,key,lg) {
        if (someWebAppCondition) {
            var n = ns+':'+key+'.'+'FOO';
        } else {
            var n = ns+':'+key+'.'+'BAR';
        }
        return i18n.t(n);
    },
    [.... other init options ....]
});
```

* html

```
<p data-i18n="myNameSpace:myKey"></p>
```