Publicly thank contributors on a video

## User story

As a major contributor on a specific video (statement collection, comments... **to be determined**), I'd enjoy having my name mentioned on top of the statements list.

## Best solution for this problem

We can define different types of remarkable contribution on a video. For instance:

* Having collected at least N% of all the statements
* Having commented (only confirmed/refuted?) at least M% of the statements

As soon as a contributor made a remarkable contribution, his name is mentioned on top of the statements list.