Improve roadmap structure to fix localization process

As i explained in #1039 (comment 8958) at the moment is impossible to the keep the roadmap updated for all languages. The current structure doesn't scale with a multilingual website. I suggested some solutions in the comment, but i found a different and easy way to fix the problem which doesn't require external script or tools. I will add some some CSS and completely change the lang/LANG/roadmap.yml files. The resources/roadmap/index.md page will be heavily changed as well. It will basically be a refactor with few cosmetic changes (including #1057 (closed)).

Opening this mainly for tracking, because it will take a good amount of time to implement. A similar system could probably work for the user guides as well, but that will require some more testing because there is much more stuff to take care off.