Add Contributors page in the App

[Al12rs]

Have a page somewhere in the app listing contributors.

This is usually next to stuff like About and licenses.

In addition, make sure to include mentions to third party contributions inside app changelogs.

[Al12rs]

We can use this comment to keep track of contributions in the meantime:

• 571 @JanuarySnow

• 574 @JonathanFeenstra

[erri120]

This ties in with #465. We can use PRs to generate changelogs and extract contributors from them.

[erri120]

We should also have a CONTRIBUTORS.md file that simply lists every contributor: https://github.com/jellyfin/jellyfin/blob/master/CONTRIBUTORS.md