* Use LuaLaTeX instead of pdfTeX
Will allow to use Open Type Fonts in the future
Other less important reasons:
- Uniform encoding in UTF-8
- We could maybe use some luaTeX only packages
- It's more modern, should be better
* Use Tex Gyre Heros as helvetica clone
As it does not seem available by default on the CI machine and might
have some licensing issues.
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