Refactored intl service and private utilities

Warning

To lower the maintenance cost, I removed code that should be unused, and refactored code that should be private.

While existing tests continued to pass, it's possible that one of the refactors is a soft breaking change for your project (e.g. because you overwrote a method from the intl service). To be safe, I went with a minor release.

If you find a regression, please open an issue and provide me context, so that we can see if a revert is needed.

Thanks to @bertdeblock for fixing a URL typo in the blueprints.