Mode: Showcase

[gdude2002]

The Showcase mode should be worked on soon. It'll need to make use of #3, but work can begin before that.

The Showcase mode comprises all of Cozy's showcase channel functionality. The following list of features must be completed before this mode can be considered ready.

• Creation of managed threads for showcase posts in all channels (except for -discussion), in line with our polling
• Management commands for managing the list of external servers that are allowed to add the bot
• User commands for publishing messages to Quilt's showcase channels from their development server
• User management commands for setting up auto-publishing
• Database storage of showcase message metadata to allow for the processing of edits and message removals