Stop displaying past challenges to participants.

[guyandtheworld]

Fixes #35

[coveralls]

Pull Request Test Coverage Report for Build 215

• 2 of 2 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.03%) to 90.554%

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Totals
Change from base Build 199:	0.03%
Covered Lines:	278
Relevant Lines:	307

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💛 - Coveralls

[RishabhJain2018]

@isht3 I think you should also check that if the challenge is approved_by_admin and publically_available then only it should appear in this list, otherwise it will create discrepancy in the data on UI and in cli. Think of a case where a host hosts a challenge and a participant participates in it but due to some reasons he has to disable the challenge then the challenge won't be available on UI but it comes on cli. Do you see what I mean here? Feel free to ask doubts if you have any.

[guyandtheworld]

@RishabhJain2018 Yup understood

[guyandtheworld]

@RishabhJain2018 I've made the changes to incorporate that, can you check?

[RishabhJain2018]

@isht3 any update on this?

[guyandtheworld]

@RishabhJain2018 Updated with test cases.

[guyandtheworld]

@RishabhJain2018 Changed!

[RishabhJain2018]

@isht3 One merge conflict :P

[varunagrawal]

Rebase! and LGTM.

[guyandtheworld]

@RishabhJain2018 @varunagrawal Done!