improving language chooser

Related to https://github.com/coopdevs/timeoverflow/issues/92

![captura de pantalla 2014-12-03 a la s 01 41 31](https://cloud.githubusercontent.com/assets/576701/5273884/9618674c-7a8d-11e4-9016-d1f1707c4fa2.png)

```ruby
link_to_unless (I18n.locale == locale), switch_lang_path(locale: locale) do ...
```
para evitar que genere el enlace.

De hecho, podríamos generar el trozo de paréntesis por css y simplificar esto:

```ruby
link_to_unless (I18n.locale == locale),
               t(locale_key, locale: locale),
               switch_lang_path(locale: locale),
               data: {localized: t(locale_key)}
```
y
```css
#language-chooser a[data-localized]::after {
  content: " (@attr(data-localized))";
}
```