[FEATURE] ass custom themes

[Facinorous-420]

Description

So far editing ASS' index is super easy since you just throw a .js file in the share folder with a small route code and call it a day.

Though, there are 2 things I noticed that could be enhanced to follow this same concept:

1. The viewer's view file. Allow people to easily edit what this looks like by having the ability to let the user redirect to a custom viewer.
2. The ability to easily customize the color scheme in the tailwind config.

[tycrek]

Initial theming support detailed on the README https://github.com/tycrek/ass#customizing-the-viewer

So far I think that covers point 2. Point 1 will take some more work.

[tycrek]

Will refocus a theming system for 0.15.0

Also focus on Highlight.js presets (or similar), see #141 for more info