Evalai: Add countdown timer for the challenges

[RishabhJain2018]

Current Behaviour:

There is no timer shown when the challenge deadline is approaching.

Expected Behaviour:

There should be a counter which will automatically appear one month before the challenge deadline.

Reference: #1769

[RishabhJain2018]

@Sanji515 Would you like to work on this?

[Sanji515]

@RishabhJain2018 Sure!

[Sanji515]

@RishabhJain2018 @galipremsagar Hey, In general, I'm thinking of UI for countdown timer something similar to this please take a look at the screenshots.

Or we can remove the background

[galipremsagar]

2nd one looks better but Look into this: http://flipclockjs.com/faces/daily-counter
FlipClock looks nice and we can theme it accordingly to our UI color.

[stale[bot]]

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