Make Batman.I18N filter work correctly

I make some change and let `t` and `translate` filter can work correctly.
This also support `interpolate`-like behavior which can pass some variable and combine into a string.

But I still have some problem about I18N support:

* `Batman.I18N.enable()` will stop `/locale/en.json` load, but if using rails it will cause user can't load all translation. (relate this issue: https://github.com/batmanjs/batman-rails/issues/52)
* When user switch locale, wait translation load from server, the webpage may flash due to new locale is null before downloaded. ( This can provide default locale fallback to improve it, I will add it soon. )

And something todo:

`Batman.helpers.interpolate` will run twice, this can improve by rewite `@translate` method.