Fix leaderboard column inconsistencies

### Description
This issue is similar to #3331 and has been reported by our current users.
The leaderboard has CSS inconsistencies because of which the column names do not appear properly when there are several columns.

### Pre-requisites/Learnings
This issue essentially requires background on a few things:
- An overall understanding of the models related to [Challenges](https://github.com/Cloud-CV/EvalAI/blob/master/apps/challenges/models.py) on EvalAI.
- An understanding of the [EvalAI frontend](https://github.com/Cloud-CV/EvalAI/tree/master/frontend).

### How to Approach
- You can start by setting up EvalAI locally. Set up the dev version locally (preferred) using the steps [here](https://github.com/Cloud-CV/EvalAI/tree/master#installation-instructions).
- Create a challenge locally using GitHub starter template with `ngrok`. This will need some reading.
- One possible solution is given on the above mentioned issue. Feel free to experiment with the frontend locally and open a PR with screenshots.
- Reach out to us regarding any issues that you face or if you need any help with understanding any of the above.