Use favicon.js to show notifications count on favicon
<!--IssueSummary start-->
<details>
<summary>
Everyone can contribute. [Help move this issue forward](https://handbook.gitlab.com/handbook/marketing/developer-relations/contributor-success/community-contributors-workflows/#contributor-links) while earning points, leveling up and collecting rewards.
</summary>
- [Close this issue](https://contributors.gitlab.com/manage-issue?action=close&projectId=278964&issueIid=14990)
</details>
<!--IssueSummary end-->
Use Favicon.js (http://lab.ejci.net/favico.js/) to show notifications (new commits on projects, issue updates, etc...) count on favicon.
issue