Update text and refs in API and authentication
Add figure generation

Figure generation depends on LuaTeX and ImageMagick. The figures are
written in LaTeX with the tikz package and can be hard to generate.
For now I (Malthe Jørgensen) will generate them when needed, but in
time a better generation mechanism will hopefully be set up.
Read figures from JSON instead of hardcoded

The JSON file allows for size specification
also added README for the figure generation
Add LanguageCode to metadata description