Removed all _data/LANG/roadmap.yml files and moved all strings to _i18n/LANG.yml to take advantage of the multilingual
plugin. Also removed all loops in resources/roadmap/index.md, now we simply map to each placeholder.
This commits removes the page 'Technical specs' and adds some technical info to the 'About' page.
The 'technical specs' folder and page were removed from the repo, from the navigation menu and
the footer (for all languages)
- changed format of roadmap.yml back to UTF-8
- fixed various formatting issues in nl.yml and added missing keys
- change encoding of all user guides (nl) to UTF-8