Lacking feature parity for new patchnotes website

## Description of the Issue
The new patchnotes website has some missing features compared to the old one which make it worse to use.
For example comparing https://faforever.github.io/fa/changelog/3810 and https://patchnotes.faforever.com/pages/balance/2024/3810.html:
- [ ] No dark theme
- [ ] No table of contents to click to navigate around
- [ ] No icons for particular changes

Looking at https://patchnotes.faforever.com/:
- [ ] No themed background with game screenshots

## Possible changes
- Theme button in the bottom right to swap between themes.
- When opening a changelog for a version, the dropdown on the left (which is currently broken) could expand to show the sections (balance, other, feature, etc) of the changelog.
- Since a typical dropdown would have "Changelog page -> every single game version -> sections of version being viewed", which takes up a huge amount of space, it could be compressed into "Changelog (version#) -> sections of version being viewed". The "(version#)" text would be grey and only appear while viewing a version page.
- Maybe unit icons could be grabbed from the generated github wiki, with unit ids or enhancement icon IDs as references in the snippet. The goal is to give an easily accessible (from the PR author's perspective) way to add an appropriate icon for significant changes into a snippet.

## Additional Context
The old patchnotes website repo is here:
https://github.com/FAForever/patchnotes