Rate limit for exercise submissions

[nygrenh]

• rack-throttle, 15 submissions per 10 minutes
• 250 per day [user_id] -> ban time 24h
• another limit for those with many submissions:
  • 3 per 10 minutes Lower submission priority Submission.where(created_at: (Time.now - 10.minutes)..Time.now, user: current_user).count

[Redande]

Rack-throttle: https://github.com/testmycode/tmc-server/commit/105d04082fc0f6f63159c9046872ad021ba21612 Low priority: https://github.com/testmycode/tmc-server/commit/75bf4f3c1105088469c243abd3f48da5347b07d2