bunch of additions

[flypenguin]

sorry for packing this all in one pr, i thought i'd just try. i added a bunch of stuff and updated the docs.

in detail, roughly sorted by impact:

• add matomo analytics integration
• added remark42 comments engine (unfortunately dependent on the cactus comments "fix")
• fixed that the cactus comments script is not included/loaded if cactus comments are not enabled
• add a switch for disabling the page gallery (which is really annoying if you want to include images)
• add an option for an <hr> element before comments

should all be tested, at least it works on my site :) .

[netlify[bot]]

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[RobbiNespu]

+1