Add competition scores feature

[Manitary]

Add a way for users to record their competition results to share and compare

• [x] Add command to submit a competition result
• [x] Add validation/rejection of user submissions by admins
• [x] Add command to retrieve own global best scores
• [x] Add command to retrieve own best scores of a competition
• [x] Add command to retrieve the leaderboard of a competition
• [x] Add command to delete all own scores
• [ ] (unsure) add command to retrieve scores of another user