Server archive/backup command

[rubellyte]

A plugin that provides a command to dump and archive all messages on the server it is executed on.

Expected functionality:

• Plugin will scrape any channels it can read and collect a complete message log.
• Plugin will create human-readable message logs for each channel it scrapes.
• Plugin will create a data JSON file containing information about the channel, as well as raw message data, including IDs, authors, reactions, reply-tos, etc
• Plugin will scrape and save data about the server and its members, including guild name, channel structure, profile data, etc.
• Plugin should gracefully handle errors including lack of permission and missing files and continue processing, while providing an error message to inform the user of the issue.

Additional possible functionality:

• Plugin will optionally scrape and download all message attachments instead of saving links to them.
• Plugin will optionally scrape and download all user avatars.
• Plugin will provide a warning if it cannot read all server channels, prompting for confirmation before starting the archival.
• Provide a tool that can parse the data files in the archives and produce a readable Discord-esque HTML page for viewing.
• Allow an archive to be updated without re-scraping the entire server.
• Dumps over a certain filesize can't be uploaded to Discord, and instead need to be saved to disk and fetched by the bot maintainer. Look into some ways to mitigate this issue?