Before doing this, we need to think through any issues that will be caused by adding new system emojis such as:

• If a system emoji is added that has the same name as a custom emoji that already exists, what will happen?

• What happens if the apps are out of sync on what emojis they think exist? Notably, if the mobile app expects emojis that the server doesn't have, we need to still render them at least somewhat properly.

• Are there any other issues that need to be considered here?

Updating the list of emojis will require:
1. On a version of Mac OS running the latest version, update `emoji.js` and `emoji.json` for the mobile and web app repos using the script found at `build/emoji/make-emoji` in the web app repository
2. Generate emoji_data.go for the server based off emoji.json. This comment contains a Go snippet that should be able to do that

Also needs to update the library for unicode emojis in the push proxy server