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
locales.each do |locale|
  concat content_tag(.....)
end
```