Anti-raid features

[eepykate]

• automatically assigns a role (functionally similar to muted) to all members joined after !raidon, and maybe for a few minutes before.
• enable slowmode on all channels
• set moderation level to "high" (no messages for 10 minutes after joining)
• easily mass-ban(/kick) (should delete all recent messages too)
  • join time
  • regex name matching
  • account age
  • or any combination thereof

The first three should be reverted whenever !raidoff is ran.

This should be triggered automatically whenever a large amount of people join within a short time period.