Configuration option for TOC display

Fixing change request #79

Localisations for new admin mode colors

Localisations for dark mode highlight colour

Make sure it looks right in the template style settings.

Translation plugin support

Finalizing support for the translation plugin, including dark mode styles and other touchups

In-page links update

Removed icon for in-page links, added config colour for inpage links, both for normal and dark mode.

New Style property: Headline fonts

new properties "headline_fonts" and "alt_font_size" for separating the two (WIP)

Removed letter-spacing option

This option did not contribute to better legibility, but instead broke other layout options.

Print styles updates

Improvements to print styles. In particular, the two-columns style is now optional, but much improved.

Also a minor fix for PHP 8.0 compatibility.

Accessibility Fixes

Some minor accessibility improvements, mostly to make sure the default colours come with enough contrast, even in certain edge-case situations (e.g. links in table headers)

override homepage link

New configuration option to allow overriding the homepage link.

Languages Updates

Rebuild of the translations for five manageable languages.