Multiple providers for video

# Description

A lot of publishers post their videos on both Facebook and Youtube. We should be able to have multiple URLs for videos.

This could be done by changing `videos` table to work like that:

```
youtube_id: string,
facebook_id: string,
vimeo_id: string
```

When returning from the API, `url` field should contain a default URL (either youtube or facebook) but also the different provider's ids.

We should also add a `{provider}_offset` column for each provider that will allow to set different offsets for each provider.

We will keep the legacy `provider` and `provider_id` columns until all the projects are migrated.

# Progress

- [x] Frontend
- [x] Backend
- [ ] Extension
- [ ] Injector