Add figure previews and fix Zotero-related issues with bib parsing

[cochaviz]

Now also shows table, figure, listing and equation previews in the documentation tab in cmp. Also fix some Zotero-related issues with bib parsing (in Zotero {{}} are added around certain words to add emphasis, but I've decided to just ignore these).

Screencast.from.2023-12-23.14-43-48.webm

The I thought about creating my own regex strings to fix the bib matching, but the ones from the related project https://github.com/aspeddro/cmp-pandoc.nvim/tree/main work very well. Since this is licensed under the MIT license, I've added the appropriate credits there.

I'm also working on a latex preview for the equations, but I'm still working on that. (Just wanted to mention why the latex_preview function is empty).

EDIT: Latex previews now work (using nabla like cmp-pandoc, but implemented slightly differently).

[cochaviz]

Turned it into a draft since my naive implementation is a bit too naive. Will try using the found references as indexes and pattern matching on the reversed string from a match.