Add method to load a localised bundle

[cdjackson]

This adds a method to access a localised bundle.
This is used to allow me to use angular-localization to load a complete bundle into another package which has its own i18n system.

I see there is also a request for this, or something similar here so this might also cover this request.

[cdjackson]

To use, you need to call -:

ready("bundle").then(function() {
  localised_bundle = locale.getBundle("bundle");
})