Numbering in PDF export is broken

Heading numbers in PDF export are broken in the most recent version 1.10.0, all numbers that are not explicitly set are 0.

From a first analysis, it seems that paged.js tries to be clever and handle CSS counters itself even though this is no longer necessary with the new code. This handling of counters doesn't support counter-set and probably also not counter-increment on before pseudo elements even though this is part of basic examples.

However, it seems that NCAPP-84 is not affecting paged.js as apparently paged.js is not following the CSS counters specification. For this reason, we could get away with using the old CSS that is meant for browsers without counter-set support when paged.js is active. The remaining question is how to ensure that the new CSS is not applied on paged.js.