Restructure scripts.irssi.org to source directly from other repos

I would find it really useful to have scripts.irssi.org only have small meta-data-blocks per script, describing how they should be sources from external sources like git repos and such. A bit like how https://github.com/melpa/melpa does it for emacs packages.

Start by inspecting the repository structure and comparing the proposed metadata-block approach with the MELPA model linked in the issue. Determine how scripts are currently represented and sourced, then define the metadata and external-source workflow needed for the site to source scripts from other repositories.

Written by the indexing model from the issue text.