Support updating/replacing emojis in the custom emojis settings page

As of version 1.6.1, there is no option to replace the image of an emoji. Current behaviour Suppose we want to change the image of the custom emoji :example:. We would need to delete the :example: emoji altogether, then create a new :example: emoji and upload a new image. The new emoji image won't be used automatically in all Outline pages already using the :example: emoji, we need to also manually edit every page already using the emoji. Updating the image of an emoji is not something that happens often, but when it does the whole process is tedious. Proposed solution It would be amazing if the admin page for custom emojis would not only allow adding and deleting emojis, but also updating existing ones. …