Fix warnings

[koppor]

• "Command \@parboxrestore has changed."
• "csquotes should be loaded after fvextra"
• filecontents is obsolete
• eq:test multiply defined
• eq:test@cref multiply defined
• footnotehyper warns about: "The footnote environment will not be fully functional, sorry."
• pgfplots wants to be updated to compat 1.17 from 1.14
• Use of \deftripstyle should be replaced with \deftriplepagestyle
• center environment in figure
• 4 nag warnings and missing font shapes.

Fix or add an ADR.

[Vogel612]

The changes to @parboxrestore as well as the csquotes loading are connected, but neither is really fixable, since the root cause is loading minted after csquotes. Considering that only the -minted files should load it, it cannot be moved into the config and pushing csquotes into all four tex-files seems like a bad decision.

filecontents is loaded by latexdemo, so I doubt we can fix that.

I have no clue why footnotehyper is complaining, so I unfortunately can't even attempt to fix it.

The pgfplots compat setting is noted to be used for overleaf support. I personally would not mind dropping that support and just forcing compat=latest, but that seems a more complex issue.

Some other fixes are in #136