Add CapyPDF · 9889219c

Building CapyPDF needs to be singled out because of its C++23 build
requirements.

We also move from "standard libjpeg" to "turbo jpeg" as CapyPDF wants
an ICC related function which is not present otherwise. That in turn
requires to finally migrate from ImageMagick v6 to GraphicsMagick
because that was holding us on the "standard libjpeg".

Switch boost to cmake build · 95871a06

This gets rid of our previous hackish-way of installing it and
finally integrates it nicely with out JHBuild setup.