rewrite github related code

[onerandomusername]

Summary

Rewrite the entirety of GitHub issue/pull handling code.

closes GH-571
closes GH-320
closes GH-564
closes GH-564

Key refactors

• use a renderer system for each type of resource having a class based renderer, rather than a whole bunch of Ifs
• centralized configuration for all behavioral changes by any configuration or feature set
• standardized behavior
• removal of the show more/less button, replaced with the show more button which shows a modal rather than more contents
• smaller limits on the size of the embed
• proper mixing of different types, such as a link and shorthand in the same message
• properly follow and display source repository when an issue/discussion has been transferred to a different repository
• mirror the emoji colors to the embed colour
• when displaying comments, use the same coloured embeds that Discord webhooks use.
• provide the correct html_url for mannequin users
• provide the correct username/login for mannequin users on comment embeds

[onerandomusername]

Hashing issue with ghretos classes. Need to reconstruct all of them to hash with the variables used in the url.