Implement leaderboard system for signed up users

[sb-decoder]

1. leaderboard button should be enabled after sign in.
2. leaderboard should be based on average score with same number of matches.
3. If different number of matches then higher match leads to higher position in leaderboard.

[venkatasaimohit]

@sb-decoder please assign this to me

[shashwatsingh07]

@sb-decoder i want to work on it , can u please assign it to me ?

[Arnab-dot]

@sb-decoder I would like to work on this issue. Can you please assign it to me ?

[sb-decoder]

#126 (comment)

@venkatasaimohit, if you are still working on this, take a look at the above issue, and make sure to implement the leaderboard topic wise.

[DeshDeepakKushwaha]

can u assign this to me

[Atharvverma1234]

Hello,
I would like to work upon this issue.
Please assign it to me.