Organize fact-checking rushes

[Vayel]

User story

To stimulate the contributors, we could organize fact-checking periods during which the reputation gains are doubled (to be determined). For instance, we can say: "if an action is performed at most 24h (to be determined) after the video was published, all the gains received for this action (through positive votes) are doubled".

Related to #59, we can split this period into two parts:

1. The reputation gained from statement collection is doubled (so that people first focus on collecting statements rigorously)
2. The reputation gained from upvoted (sourced, to be determined) comments is doubled

[Betree]

This would be really useful for live videos. It would also be a way to feature old videos that needs participation.

We've just discussed it with @CaptainFact/ambassadors and that's something we want to do, let's add it to the roadmap.