Add custom emoji to award emoji picker

In &3966 (closed) we've added the backend changes to make it possible to upload and create custom emoji.

Now some frontend needs to be done to add those emoji to the award emoji picker as well.

There were already made some efforts to make it easier to implement this, see &278.

Implementation detail

TBD

Availability and Testing

Additional feature spec to be added where a user adds a custom emoji and then selects the custom emoji as an award and also within a comment.