challenge-page fixes

[ayu-ch]

Some fixes and additions to be done for the challenge page (both contestant and admin side):

• Add all challenges filter
• Add redeeming of hints
• Add challenge score in challenge card.
• Error handling in redeeming hints. (fix on backend too)
• Allow the contestant to see who have solved the challenge, other than just number of solves (low-priority).
• Don't show input if the challenge is solved.
• Allow admin to view hints without having to redeem (need to fix on beast too)

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• Allow admin to filter and search through submissions (low-priority)
• Show and filter cheating submissions admin side.