Update Category Headers scripts

[ValerioLyndon]

Category Header scripts need updating. This should probably include splitting them into their own repository.

Specifically, they need:

• [ ] Easily customisable CSS template to make it more dynamic.
• [ ] A built-in menu on the list page for easy installation/modification of aformentioned templates.
• [ ] (?) Automatic addition of the required styling CSS
• [ ] (?) To create their own header elements instead of relying on CSS. For example, instead of using .data.stats.watching::after you would have a whole new element in the list table: <div class="list-header">Watching</div>. This has benefits and drawbacks.

The files in question: 1 2