multiple contests

[rishabhKalakoti]

• made a basic system for multiple contests
• made a basic UI for multiple contests
• dummy contests to be added manually as of now
• contest timings not covered in this PR
• exception handler missing
• same question set copied again to have more questions for testing

fixes #106 fixes #107

[theSage21]

This is beautiful work. :+1:

Some stuff needs to be filled out. Would you like to do it as separate issues or within this PR? Here are things that come to mind:

• [x] reusing questions per contest is actually a good idea
• [ ] leaderboard calculation needs to change for each contest
• [ ] leaderboard calculation needs to only count questions which are in the contest

[rishabhKalakoti]

I was planning to go like: multiple contests > contest timings > leaderboard one by one to keep things simpler