Create challenge configuration using CLI

Users should be able to create a challenge configuration zip using CLI. The idea is to have a similar setup that Sphinx provides when you want to generate the documentation configuration. It should work something like this:

Command: `evalai create_challenge`

```
$ evalai create challenge

Enter the challenge name:
Test Challenge

Enter the Number of Phases:
2

Enter the Phase 1 name:
Test Phase

Enter the Phase 1 codename:
test-phase
.
.
.
.
.
.
```

CC: @isht3 @varunagrawal @RishabhJain2018