Allow locales to be selected programatically

Seeks to address rmm5t/jquery-timeago#173. Takes the approach used by
@jgraichen (see this
[patch](https://github.com/jgraichen/rails-timeago/blob/master/scripts/j
query.timeago.js.patch) and the [converted locales
here](https://github.com/jgraichen/rails-timeago/tree/master/vendor/asse
ts/javascripts)).