Reimplemented cog menu for managing signups

[JacksonVirgo]

Added the cog menu back from the old version.

• Creating categories
• Deleting categories
• Updating categories
  • Rename
  • Change limit
  • Add users
  • Remove users
  • Cull users that left the server (as they cannot be fetched via a user select menu)
• Toggle anonymity
• Change name of signups
• Signup logging using webhooks