Feature/worker monitoring

[IdirLISN]

A brief description of the purpose of the changes contained in this PR.

Adding button inside the edit section of competitions, participant page, to create groups of users linked to a queue.

In edit section of competition, we can now create groups for this specific competition, edit groups, add participant to groups and associate a queue to groups.

If a user is inside multiple groups when he submits, multiple child submission are created (1 per group).
Each child submission are displayed in lines inside of the leaderboard ordered by ranking.

Multitasking is supported.

Issues this PR resolves

Closes #2100

/!\ new migrations files. /!\

A checklist for hand testing

• create at least two groups and assign your self to them.
• check server status if the child submissions are redirected to the expected worker.
• check UX/UI in edit page.
• check leaderboard.

Checklist

• Code review by me
• Hand tested by me
• I'm proud of my work
• Code review by reviewer
• Hand tested by reviewer
• CircleCi tests are passing
• Ready to merge

[ObadaS]

Wrong source branch, see #2393