Fulcro I18N

This is a work in progress to port Fulcro 2’s i18n support to a library for Fulcro 3. The code has been ported, but the documentation (in I18N.adoc) has not been updated.

Use at your own risk. PRs accepted, but Fulcrologic is not making this library a priority for the moment (the code has been used by commercial clients, and all tests pass, so it is likely to be fine. We don’t have time to update docs and test it).